Is there a specific rule I should be using for when to branch in source control? Branches seem to be expensive because they require that the team have extra knowledge about where the features they want to work on should go.
Our development team sometimes finds itself working on a long term feature and a shorter term feature at the same time. That means we end up with:
Trunk
-Branch A (Short Term)
-Branch B (Long Term)
After they complete we have to merge A in to the trunk, then merge the changes to the trunk back in to B to make sure those edits still function. It's messy.
I am wondering if we can cut down on branches by using Labels (Or tags, or pins or whatever your Source Control Software of choice calls it). Maybe it makes sense to branch for the longer term project, but we could just do the edits for the short term project right in the trunk after applying a label to the stable release. That way we can always retrieve the source code that was stable if we have to do an emergency bug fix, but we don't have to deal with the branch.
What rules do you use to decide when to branch?
One way to reduce branching is to implement new features (especially smaller ones) directly on trunk. This is how we do it:
small features, which will are guaranteed to be completed before the next release, are implemented on trunk
for larger features, we create a feature branch ("Branch B" in your example)
once we are ready to create a release, we create a release branch (from trunk), e.g. named "branches/2.x". This branch is then used for testing and finalizing the release.
once the release is built, we tag the corresponding revision from the release branch (e.g. tags/2.0.0).
normal development then continues on the trunk. the release branch is used for maintenance of the 2.x line of the product (e.g. bug fixes are merged from trunk, or implemented directly on that branch)
In a small team, the time to branch is when you can't commit directly into the trunk. With svn (as I guess with other version controls as well), it is possible to postpone the decision to branch till the time one realizes that one cannot commit into the trunk.
To minimize the need to branch, a new feature can be worked on in the trunk itself by restricting the new-feature code within compile-time or run-time flags. This approach also allows to later turn off feature if not needed, do A/B split testing experiments with the feature, etc.
Of course with this approach it always helps to have a continuous testing that gives an early alert whenever the build/test-suite breaks on the trunk.
For one thing, this depends on the tool you use. Branches are more 'expensive' in Subversion than in Mercurial or git, because merges are harder to do. For another, it depends on your project/organization: you should probably have at least one branch per maintained version.
It depends on the VCS you are using. If you are using a tool that has good support for merging, then you should branch whenever you feel like it. When in doubt, create a new branch. If the UNIX epoch time is even, then you should branch. If it's, odd, you should wait a second, and then branch. If you are using a tool that doesn't support merging well, then you should consider changing tools. In other words, stop using a tool that makes it necessary to ask this question.
It’s normally poor practice to develop against the mainline or trunk. The trunk should be used as the master code set and should reflect the code that currently represents production. If you are not in production yet, it should represent the gold copy and should always build and be subjected to automated regression tests. It should not be used to show development status or activity. Protect your trunk from change and resist the temptation to allow developers to check out and lock code on a trunk. The only updates in my view should be via the merge process, when you are ready to repatriate your code to the mainline.
When branching you should consider the purpose, complexity and duration of the development.
• Is it to support a team of developers working on a new feature or a substantial piece of development?
• Are you using traditional processes or the various agile flavors that are out there?
• It is to accommodate the development of a patch or fix for production?
• What development and in particular, test activity will you accommodate on the branch and will you retain the branch until the derived artifacts are built, tested and deemed releasable?
There are many models out there but few give sufficient consideration to the "build" process and the implications of regenerating your releasable artifacts.
Let’s assume you have the following lifecycle: DEV->SYSTEM-INTEGRATIONTEST->UAT->PRE-PROD->PRODUCTION. Assume you create a branch from mainline to accommodate the development and build processes. Your development\build\test cycle continues right through to UAT. The artifacts produced from this branch have been exposed to sufficient testing to deem them potentially suitable for release. You are able to state that the artifacts signed off by the users were also exposed to system and integration testing.
Some folks advocate merging the source code to the trunk at this point and recommend that you create a RELEASE branch upon a successful trunk rebuild. For me this is fine if the solution is stable and requires no further change prior to production, otherwise you risk propagating bugs elsewhere. In variably it will need to change.
If you do unearth issues in PRE_PROD, where are these “Fix” changes going to be made? Many suggest that you can make the code changes directly in the release branch. If you proceed, this modification will produce a new build and a new set of artifacts. You may elect to push these artifacts back through PRE_PROD and on to production, as the underlying code has been validated through previous testing and the modifications made to stabilize the release are deemed risk free? But you have a problem.
You cannot state that the executables\artefacts released to pre-prod and subsequently production, have been tested in your lower environments. Despite confidence being high, the output from the release branch build is different from that produced from the development builds. This may fail audit.
Branching for me is about managing your code and not the build output or solely the release. If you advocate branching for release and release stabilization (pre-prod fixing), you must take the above risk combined with the need for significant regression testing into consideration.
On the basis that the trunk should represent production code, you cannot push code to it unless it has been pushed to production first. I advocate creating a branch that supports the development, build and release as a single cycle. To avoid branch longevity and unnecessary divergence from the trunk (and potential big bang conflict issues) limit the development as much as you can and release and repatriate often with the trunk to keep other development efforts current.
Related
I was looking up good resources on branching strategies after doing feature branching for quite a few years and struggling with lots of branches and merge nightmares. Feature branches did give us a good isolation in managing releases in a pretty granular way as to which features should go to release. However, the problems they posed (many branches, merge conflicts) were way more than the benefits they gave.
We work with Oracle database (with 5000 objects) at back end. We also have multiple teams working on different areas of the same product. We are using Visual Studio with TFS (no DVCS).
The more branches we create, more database instances we require to give proper isolation in functional testing in those branches (each branch - one db instance) which are another set of problems.
We are adopting scrum and are searching for a branching model that will suit our release cycle (4 times a year) and CI builds. We are planning to do 5 regular sprint and 1 hardening sprint for each release.
From a feature branching model, we reworked our branching model to a very simple branching like below -
Development branch is working as our "Trunk" (for Trunk Based Development) and ALL developers (all teams) are committing to this branch (for quarterly release), testers are testing in this branch and CI server (Jenkins) is building this branch daily. We just need a clean MAIN at any time for safety as "Single Source of Truth for Last Release" which come to our use often for several reasons.
Maintenance branch is our bug fixing branch (hotfix) and is released several times during the year (irrespective of quarterly release). We prefer not to work directly on the main branch as want to have a "clean" Main branch. We do not want to let code go to Main without "manual" / functional testing done. Once a bug fix release is done, code is merged from Maintenance -> Main -> Development to integrate the bug fixes into Development.
We typically do not require the "Release Branches" as suggested in TBD since we will be continuously doing the bug fixes in the Maintenance branch, release from Maintenance and then merge the changes to Main (and then Development). We maintain only "Last release" and in case previous Release fix is required we create an old release branch from Labels in Main.
Have we modified the Trunk Based Development to an extent that it would pose problems in future? What are your suggestions?
Refer:
http://paulhammant.com/2013/12/04/what_is_your_branching_model
http://paulhammant.com/2013/04/05/what-is-trunk-based-development/#comment-2765204723
You should make a maintence branch from the tag that was released, only if you encounter a bug. Actually that's a release branch, and it should be named for the release. Say rel_1.1. By the time you've pushed out release 1.2 and it is clear you're not going to roll back, delete rel_1.1.
I have three environments; dev, test and staging/prod. In our previous model of using Team Foundation Server, we would have three branches of code that matched up to each of these three environments.
Developers would work locally and when they had their code complete, they'd check it into the dev branch. When checking in, TFS automatically creates something called a changeset. This check-in would kick off a build of the files into code which then gets deployed to the dev environment.
When a developer was happy with their code in dev, they'd merge just their changeset into the test branch. They'd pull up a complete list of all of the available changesets that dhad not been merged into test, they'd select theirs and check those into the test branch. Again, this would kick off a build and the output files would get deployed to test.
Once QA was happy with the changes, the dev would merge this changeset into the prod branch. Kicking off a build and the files would be deployed to the staging area. The developer and QA would them promote these files to prod.
All of would allow multiple developers to work on the same files using this changeset mentality. When a specific changeset (or set of changesets) was merged into another environment, only those changes would get merged.
In my relatively new exposure to git, I cannot seem to find a way to select specific "pull requests" (which I assume is similar to a TFS changeset) from one branch to another branch. When I try to make a pull request from one branch to another branch, it wants to pull in not only my pull request, but every other pull request made in the lower branch by other developers too. What is the magic way to make this happen?
Note: Unfortunately we don't have the notion of a "release". We have five scrum teams working on one website with over 200 pages. Each scrum team has their own sprints and can release multiple scrum stories during their sprint. We have internally only one DEV environment, and one TEST environment and one PROD environment. Not only are our environments used by these five scrum teams, but these DEV/TEST/PROD sites are is also used by various other teams for integration efforts with applications we sell and also for customer account management and purchasing. We cannot change that infrastructure.
Note: this is not for a discussion as to if this "changeset" methodology is correct or proper. This is a question of how to achieve this behavior in github/git.
Note: we are a set of scrum-based agile teams. We work from stories. As many as 60 stories can be actively in development at any one time with our large team of 25+ developers. When one story is ready for prod, we promote it to the prod environment as an atomic unit. So think of a changeset as a story.
I have two thoughts:
Don't do it this way. Instead, you should look to git-flow. http://danielkummer.github.io/git-flow-cheatsheet/ and http://nvie.com/posts/a-successful-git-branching-model/ are good explanations. At it's core, git-flow is a naming convention for branches, so it's really not tied to git at all. In essence, you have feature branches that each developer or dev team works on. Once they complete a feature, they merge into develop. develop is "done features" -- not "done done" but rather "feature complete." When we deem it time to release, we fork to a new release/someversion branch (name to match the release name), and then work with QA to harden the release. Commits on the release/someversion branch are only bug fixes. Once it's good enough to deploy, we fast-forward the master branch up to the release branch as we push it into production. master then represents what's in production. As we deploy, we also merge release/someversion into develop so the bug fixes get into the mainline of development. The project manager / product owner can then think of the develop branch as "the latest," and developers can continue on their feature branches until they're feature complete. (Hint, make features small -- like an hour or a day. Features are not releases.)
So why is this better than the way you were doing it? If the feature is done, ready enough for QA to start banging on it, it's done enough to be part of the next release. Picking and choosing features around each other will lead you into very subtle and unpredictable bugs. Since you're re-merging at each step, you have the possibility that you'll merge incorrectly, creating a bug. You're also now creating unique product with each step, so you could get to production with a completely different set of features than you vetted in dev and test. (Will this do bad things? Ask your pharmacist if these drugs interact when taken together.)
Git-flow works great for cadences where you have well coordinated, infrequent, larger releases. As you get closer to continuous delivery, this ceremony will get in your way. At that point, you may choose to flip to GitHub flow or a similar lighter-weight naming convention.
If you're really, really, really (see the above "you shouldn't do it this way" comment) convinced you should do it this way, first, go convince a rubber duck and hopefully you will have talked yourself out of it. If you're still really, really convinced you need to do this, you'll frequently need to squash your commits together creating one large commit for the entire feature, then cherry pick the changeset between the branches.
There's a few disadvantages to this "squash and cherry-pick" approach. 1. You lose history. Since you're squashing the history together, you have to now keep features in very contained bundles, and frequently edit the bundle as a whole. One of the primary premises of source control is you get an audit history -- both to roll back to if something goes wrong, and to reference when you need to learn why something works this way or who to talk to about it. (See "git blame".) When you squash, you intentionally remove that learning tool. 2. You're playing features into place in different orders. So you're frequently doing merges. What makes git so awesome is merging is easy. What makes git merging easy is you do it in small pieces. This methodology of squashing everything associated with this feature into one huge commit and cherry-picking it between branches means you're doing very large merges ... which means it will be hard.
Yeah, I know you're quite enamored with the way it's always been, and you really don't want someone telling you your baby is ugly. Sorry. Your baby was ugly. On the bright side, it doesn't need to be. Git flow is awesome, and can definitely facilitate the velocity your team needs.
You previous behavior was dysfunctional. Although not unusual: http://nakedalm.com/avoid-pick-n-mix-branching-anti-pattern/
In Git you most likely want to do two things. The first is to follow Git Flow: http://nvie.com/posts/a-successful-git-branching-model/
Once you have this you can look at creating a deployment pipeline for binaries, not for source. You should do a build from MASTER and that build goes through your environments. Happy to discuss here and offline.
We use a JIRA as our ticket system. New bugs/tickets are submitted to that system. Once a bug is fixed, we create a new build and test it on our dev server. If everything is good we push it to the live server. Now I usually work on the trunk without any branching to fix the bugs. This is of course a problem. Because there can be many bugs in our system, but only certain ones get fixed at a time. However if I fix all of them in the trunk instead of a branch, then we are forced to test them all even if we did not had enough time to test them all. How do you usually fix bugs and branch etc..? (I am not sure if I explained it very well).
Here is the strategy I use. I develop in the main trunk. When the software is released, I branch it (say v1.0). When bugs come in, fix in the branch trunk and then merge back to main trunk. Here is a good synopsis of strategies that are available: http://www.cmcrossroads.com/bradapp/acme/branching/branch-structs.html
I'm not sure if it's the normal strategy but we do all work on the trunk and then backport bugfixes into release branches. Our main trunk is always 'unstable' and when we feel we have a trunk in a releasable state we branch it into a release branch. From then on buyfixes are ported back into the release branch and new functionality only gets added to the trunk. It means you can run your release branch through testing and focus on testing the bugfixes.
One common mode of operations is that the deployed software lives in a separate branch which receives only bugfixes. Where you actually develop those fixes is mostly irrelevant; to avoid interference with the current development, it makes sense to develop the fix on top of the "live" branch, then test/commit/deploy to the live system and aftewards merge the fix back into the trunk.
We have the same problem (or almost), and I think every developer team has it. I can unfortunately not yet give you an answer by experience, but only a theoretical one.
In my opinion, as long as it's a bug fix, it should be deployed as soon as possible.
What I am about to implement is a feature branch strategy, and a release branch.
This means we have to differentiate features from bugs. and what is deployed is branched separately (or labeled, in our case)
Doing this, you can still work on the trunk for the bugs, and deploy them to your testing server, and once it's tested and approved branch it to the release branch and deploy it.
you can also merge-in the bug fixes into your feature branch, or try to merge the feature later when you plan to deploy it to the testing server.
Anyway, the most important I think is to branch the long work that prevent you from deploying smaller bug fixes.
If you branch too much, you will have a merging problem. If you don't branch enough, you will have a deployment flexibility issue.
It depends on your version control system. If you're using git, where branches are cheap and merges are easy, then I would definitely create a new branch for each fix. This allows you to keep bug fixes independent of each other, allowing greater flexibility with respect to what gets merged into the master/trunk, and when.
On the other hand, if you're using Subversion, branches are more expensive (in terms of creating and switching/updating) and merging is more difficult. Often the cost/benefit ratio of a new branch isn't high enough (especially for small bugs) to make it worthwhile.
I wouldn't recommend branching on every reported bug. As you said, you may not decide to fix every bug that's reported, which would mean that you'd have a lot of dead branches to prune at some point.
If your tools & language support it, branching on every bug you decide to fix (and feature you decide to implement) isn't a bad idea. It allows you to develop and test each bugfix/feature when you have the budget and schedule to do so, and merge them back into trunk when you are ready.
We split our branches into product versions / release, so that each release has its own branch. The release from the branch is tested, and so we only need to test the fixes applied to that branch.
Additionally each product version has a dev and a main branch. Developers are allowed to freely commit to the dev branch without fear of interfering with the Release (only other developers!)
Unless you're using a distributed SCM (Mercurial, Git, ...) where branching is basically free, branching on every bug sounds like an unreasonnable amount of work.
The usual strategy with central repository SCM is to note the revision that is supposed to fix the bug, and test against a build made with a later revision. You can then merge the concerned revision back into the release branch.
We are using mercurial, and branching to fix bugs and then merge changes back is quite doable in a distributed SCM
Our policy when delivering a new version is to create a branch in our VCS and handle it to our QA team. When the latter gives the green light, we tag and release our product. The branch is kept to receive (only) bug fixes so that we can create technical releases. Those bug fixes are subsequently merged on the trunk.
During this time, the trunk sees the main development work, and is potentially subject to refactoring changes.
The issue is that there is a tension between the need to have a stable trunk (so that the merge of bug fixes succeed -- it usually can't if the code has been e.g. extracted to another method, or moved to another class) and the need to refactor it when introducing new features.
The policy in our place is to not do any refactoring before enough time has passed and the branch is stable enough. When this is the case, one can start doing refactoring changes on the trunk, and bug-fixes are to be manually committed on both the trunk and the branch.
But this means that developpers must wait quite some time before committing on the trunk any refactoring change, because this could break the subsequent merge from the branch to the trunk. And having to manually port bugs from the branch to the trunk is painful. It seems to me that this hampers development...
How do you handle this tension?
Thanks.
This is a real practical problem. It gets worse if you have several versions you need to support and have branched for each. Even worse still if you have a genuine R&D branch too.
My preference was to allow the main trunk to proceed at its normal rate and not to hold on because in an environment where release timings were important commercially I could never argue the case that we should allow the code to stabilise ("what, you mean you released it in an unstable state?").
The key was to make sure that the unit tests that were created for the bug fixes were transitioned across when the bug was migrated into the main branch. If your new code changes are genuinely just re-factoring then the old tests should work equally well. If you changes are such that they are no longer valid then you can't just port you fix in any case and you'll need to have someone think hard about the fix in the new code stream.
After quite a few years managing this sort of problem I concluded that you probably need 4 code streams at a minimum to provide proper support and coverage, and a collection of pretty rigorous processes to manage code across them. It's a bit like the problem of being able to draw any map in 4 colours.
I never found any really good literature on this subject. It will inevitably be linked to your release strategy and the SLAs that you sign with your customers.
Addendum: I should also mention that it was necessary to write the branch merging as specific milestones into the release schedule of the main branch. Don't under-estimate the amount of work that might be entailed in bring your branches together if you have a collection of hard-working developers doing their job implementing features.
Where I work, we create temporary, short-lived (less than day -- a few weeks) working branches for every non-trivial change (feature add or bugfix). Trunk is stable and (ideally) potentially releasable all the time; only done items get merged into it. Everything committed from trunk gets merged into the working branches every day; this can be largely automated (we use Hudson, Ant and Subversion). (This last point because it's usually better to resolve any conflicts sooner than later, of course.)
The current model we use was largely influenced by an excellent article (which I've plugged before) by Henrik Kniberg: Version Control for Multiple Agile Teams.
(In our case, we have two scrum teams working on one codebase, but I've come to think this model can be beneficial even with one team.)
There is some overhead about the extra branching and merging, but not too much, really, once you get used to it and get better with the tools (e.g. svn merge --reintegrate is handy). And no, I do not create a temp branch always, e.g. for smaller, low-risk refactorings (unrelated to the main items currently under work) that can easily be completed with one commit to trunk.
We also maintain an older release branch in which critical bugs are fixed from time to time. Admittedly, there may be manual (sometimes tedious) merging work if some particular part of code has evolved in trunk significantly compared to the branch. (This hopefully becomes less of an issue as we move towards continually releasing increments from trunk (internally), and letting marketing & product management decide when they want to do an external release.)
I'm not sure if this answers your question directly, or if you can apply this in your environment (with the separate QA team and all) - but at least I can say that the tension you describe does not exist for us and we are free to refactor whenever. Good luck!
Maybe Git (or other DVCS) are better at handling merges to updated code thanks to the fact that they (really) manage changes rather than just compare files... As Joel says :
With distributed version control, merges are easy and work fine. So you can actually have a stable branch and a development branch, or create long-lived branches for your QA team where they test things before deployment, or you can create short-lived branches to try out new ideas and see how they work.
Not tried yet, though...
Where I work, we keep with the refactoring in the main branch. If the merges get tricky, they just have to be dealt with on an ad-hoc basis, they're all do-able, but occasionally take a bit of time.
Maybe our problem comes from the fact that we have branches that must have quite a long life (up to 18 months), and there are many fixes that have to be done against them.
Making sure that we only branch from extremely stable code would probably help, but will not be so easy... :(
I think the tension can be handled by adding following ingredients to your development process:
Continuous integration
Automated functional tests (I presume you already count with unit tests)
Automated delivery
With continuous integration, every commit implies a build where all unit tests get executed and you are alarmed if anything goes wrong. You start working more with head and you are less prone to branching the code base.
With automated functional tests, you are able to test your application at the click of the button. Generally, since these tests take more time, these are run nightly.
With this, the classic role of versioning starts to lose the importance. You do not make your decision on when to release based on the version and its maturity, it’s more of the business decision. If you have implemented unit and functional testing and your team is submitting tested code, head should always in state that can be released. Bugs are continuously discovered and fixed and release delivered but this is not any more cyclical process, it’s the continuous one.
You will probably have two types of detractors, since this implies changing some long rooted practices. First, the paradigm shift of continuous delivery seems counter-intuitive to managers. “Aren’t we risking to ship a major bug?” If you take a look at Linux or Windows distros, this is exactly what they are doing: pushing releases towards customers. And since you count with suite of automated tests, dangers are further diminished.
Next, QA team or department. (Some would argue that the problem is their existence in itself!) They will generally be aversive towards automating tests. It means learning new and sometimes complicated tool. Here, the best is to preach by doing it. Our development team started working on continuous integrations and in the same time writing the suite of functional tests with Selenium. When QA team saw the tool in action, it was difficult to oppose its implementation.
Finally, the thurth is that the process I described is not as simple as addig 3 ingredinents to your development process. It implies a deep change to the way you develop software.
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Suppose you're developing a software product that has periodic releases. What are the best practices with regard to branching and merging? Slicing off periodic release branches to the public (or whomever your customer is) and then continuing development on the trunk, or considering the trunk the stable version, tagging it as a release periodically, and doing your experimental work in branches. What do folks think is the trunk considered "gold" or considered a "sand box"?
I have tried both methods with a large commercial application.
The answer to which method is better is highly dependent on your exact situation, but I will write what my overall experience has shown so far.
The better method overall (in my experience): The trunk should be always stable.
Here are some guidelines and benefits of this method:
Code each task (or related set of tasks) in its own branch, then you will have the flexibility of when you would like to merge these tasks and perform a release.
QA should be done on each branch before it is merged to the trunk.
By doing QA on each individual branch, you will know exactly what caused the bug easier.
This solution scales to any number of developers.
This method works since branching is an almost instant operation in SVN.
Tag each release that you perform.
You can develop features that you don't plan to release for a while and decide exactly when to merge them.
For all work you do, you can have the benefit of committing your code. If you work out of the trunk only, you will probably keep your code uncommitted a lot, and hence unprotected and without automatic history.
If you try to do the opposite and do all your development in the trunk you'll have the following issues:
Constant build problems for daily builds
Productivity loss when a a developer commits a problem for all other people on the project
Longer release cycles, because you need to finally get a stable version
Less stable releases
You simply will not have the flexibility that you need if you try to keep a branch stable and the trunk as the development sandbox. The reason is that you can't pick and chose from the trunk what you want to put in that stable release. It would already be all mixed in together in the trunk.
The one case in particular that I would say to do all development in the trunk, is when you are starting a new project. There may be other cases too depending on your situation.
By the way distributed version control systems provide much more flexibility and I highly recommend switching to either hg or git.
I've worked with both techniques and I would say that developing on the trunk and branching off stable points as releases is the best way to go.
Those people above who object saying that you'll have:
Constant build problems for daily builds
Productivity loss when a a developer commits a problem for all
other people on the project
have probably not used continuous integration techniques.
It's true that if you don't perform several test builds during the day, say once every hour or so, will leave themselves open to these problems which will quickly strangle the pace of development.
Doing several test builds during the day quickly folds in updates to the main code base so that other's can use it and also alerts you during the day if someone has broken the build so that they can fix it before going home.
As pointed out, only finding out about a broken build when the nightly build for running the regression tests fails is sheer folly and will quickly slow things down.
Have a read of Martin Fowler's paper on Continuous Integration. We rolled our own such system for a major project (3,000kSLOC) in about 2,000 lines of Posix sh.
I tend to take the "release branch" approach. The trunk is volatile. Once release time approaches, I'd make a release branch, which I would treat more cautiously. When that's finally done, I'd label/tag the state of the repository so I'd know the "official" released version.
I understand there are other ways to do it - this is just the way I've done it in the past.
Both.
The trunk is used for the majority of development. But it's expected that best efforts will be made to ensure that any check-in to the trunk won't break it. (partially verified by an automated build and test system)
Releases are maintained in their own directory, with only bug fixes being made on them (and then merged into trunk).
Any new feature that is going to leave the trunk in an unstable or non-working state is done in it's own separate branch and then merged into the trunk up on completion.
I like and use the approach described by Henrik Kniberg in Version Control for Multiple Agile Teams. Henrik did a great job at explaining how to handle version control in an agile environment with multiple teams (works for single team in traditional environments too) and there is no point at paraphrasing him so I'll just post the "cheat sheet" (which is self explaining) below:
I like it because:
It is simple: you can get it from the picture.
It works (and scales) well without too much merge and conflict troubles.
You can release "working software" at any time (in the spirit of agile).
And just in case it wasn't explicit enough: development is done in "work branch(es)", the trunk is used for DONE (releasable) code. Check Version Control for Multiple Agile Teams for all the details.
A good reference on a development process that keeps trunk stable and does all work in branches is Divmod's Ultimate Quality Development System. A quick summary:
All work done must have a ticket associated with it
A new branch is created for each ticket where the work for that ticket is done
Changes from that branch are not merged back into the mainline trunk without being reviewed by another project member
They use SVN for this, but this could easily be done with any of the distributed version control systems.
I think your second approach (e.g., tagging releases and doing experimental stuff in branches, considering the trunk stable) is the best approach.
It should be clear that branches inherit all the bugs of a system at the point in time where it is branched: if fixes are applied to a trunk, you will have to go one by one to all branches if you maintain branches as a sort of release cycle terminator. If you have already had 20 releases and you discovered a bug that goes as far back as the first one, you'll have to reapply your fix 20 times.
Branches are supposed to be the real sand boxes, although the trunk will have to play this role as well: tags will indicate whether the code is "gold" at that point in time, suitable for release.
We develop on the trunk unless the changes are too major, destabilizing, or we are nearing a major release of one of our products, in which case we create a temporary branch. We also create a permanent branch for every individual product release. I found Microsoft's document on Branching Guidance quite helpful. Eric Sink's tutorial on branching is also interesting, and points out that what works for Microsoft may be too heavy for some of the rest of us. It was in our case, we actually use the approach Eric says his team does.
It depends on your situations. We use Perforce and have typically have several lines of development. The trunk is considered "gold" and all development happens on branches that get merged back to the mainline when they are stable enough to integrate. This allows rejection of features that don't make the cut and can provide solid incremental capability over time that independent projects/features can pick up.
There is integration cost to the merging and catching up to new features rolled into the trunk, but you're going to suffer this pain anyway. Having everyone develop on the trunk together can lead to a wild west situation, while branching allows you to scale and choose the points at which you'd like to take the bitter integration pills. We're currently scaled to over a hundred developers on a dozen projects, each with multiple releases using the same core components, and it works pretty well.
The beauty of this is that you can do this recursively: a big feature branch can be its own trunk with other branches coming off if it. Also, final releases get a new branch to give you a place to do stable maintenance.
Attempting to manage maintenance of current production code in line with new development is problematic at best. In order to mitigate those problems code should branch into a maintenance line once testing efforts have completed and the code is ready for delivery. Additionally, the mainline should branch to assist in release stabilization, to contain experimental development efforts, or to house any development efforts whose lifecycle extends across multiple releases.
A non-maintenance branch should be created only when there is the likelihood (or certainty) of collisions among the code that would be difficult to manage any other way. If the branch does not solve a logistical problem, it will create one.
Normal release development occurs in the mainline. Developers check into and out of the mainline for normal release work. Development work for patches to current Production code should be in the branch for that release and then merged with the mainline once the patch has passed testing and is deployed. Work in non-maintenance branches should be coordinated on a case-by-case basis.
It depends on the size of your development effort. Multiple teams working in parallel won't be able to work effectively all on the same code (trunk). If you have just a small group of people working and your main concern is cutting a branch so you can continue to work while going back to the branch for making bug-fixes to the current production code that would work. This is a trivial use of branching and not too burdensome.
If you have a lots of parallel development you'll want to have branches for each of the efforts but that'll also require more discipline: Making sure your branches are tested and ready to merge back. Scheduling merges so two groups aren't trying to merge at the same time etc.
Some branches are under development for so long that you have to permit merges from the trunk to the branch in order to reduce the number of surprises when finally merging back to the trunk.
You will have to experiment if you have a large group of developers and get a feel for what works in your situation. Here is a page from Microsoft that may be somewhat useful: http://msdn.microsoft.com/en-us/library/aa730834(VS.80).aspx
We are using the trunk for main development and branch for releases maintenance work. It works nice. But then branches should only be used for bug fixes, no major changes, especially on database side, we have a rule that only a schema change can happen on the main trunk and never in the branch.
If you are gonna be working through a release cycle, big feature, you get marooned to a branch. Otherwise we work in trunk, and branch for every production release at the moment we build.
Previous production builds are moved at that time to old_production_ and current prod release is always just production. All our build server knows about production is how to deploy the production branch, and we kick that build off with a force trigger.
We follow the trunk=current development stream, branch=release(s) approach. On release to the customer we branch the trunk and just keep the trunk rolling forward. You'll need to make a decision on how many releases you're prepared to support. The more you support the more merging you'll be doing on bug fixes. We try and keep our customers on no more than 2 releases behind the trunk. (Eg. Dev = 1.3, supported releases 1.2 and 1.1).
The trunk is generally the main development line.
Releases are branched off and often times experimental or major work is done on branches then merged back to the trunk when it's ready to be integrated with the main development line.
The trunk should generally be your main development source. Otherwise you will spend a lot of time merging in new features. I've seen it done the other way and it usually leads to a lot of last minute integration headaches.
We label our releases so we can quickly respond to production emergencies without distribing active development.
For me, it depends on the software I'm using.
Under CVS, I would just work in "trunk" and never tag/branch, because it was really painful to do otherwise.
In SVN, I would do my "bleeding edge" stuff in trunk, but when it was time to do a server push get tagged appropriately.
I recently switching to git. Now I find that I never work in trunk. Instead I use a named "new-featurename" sandbox branch and then merge into a fixed "current-production" branch. Now that I think about it, I really should be making "release-VERSIONNUMBER" branches before merging back into "current-production" so I can go back to older stable versions...
It really depends on how well your organization/team manages versions and which SCM you use.
If what's next(in the next release) can be easily planned, you are better off with developing in the trunk. Managing branches takes more time and resources. But if next can't be planned easily(happens all the time in bigger organizations), you would probably end up cherry picking commits(hundreds/thousands) rather than branches(severals or tens).
With Git or Mercurial, managing branches is much easier than cvs and subversion. I would go for the stable trunk/topic branches methodlogy. This is what the git.git team using. read:http://www.kernel.org/pub/software/scm/git/docs/gitworkflows.html
With Subversion, I first applied the develop-in-the-trunk methodlogy. There was quite some work when it came to release date because everytime I had to cherry pick commits(my company is no good at planning). Now I am sort of expert in Subversion and know quite well about manaing branches in Subversion, so I am moving towards the stable trunk/topic branches methodlogy. It works much better than before. Now I am trying the way how git.git team works, although we will probably stick with Subversion.
Here is the SVN design that I prefer:
root
development
branches
feature1
feature2
...
trunk
beta
tags
trunk
release
tags
trunk
All work is done from development/trunk, except for major features that require its own branch. After work is tested against development/trunk, we merge tested issues into beta/trunk. If necessary, code is tested against the beta server. When we are ready to roll some changes out, we just merge appropriate revisions into release/trunk and deploy.
Tags can be made in the beta branch or the release branch so we can keep track of specific release for both beta and release.
This design allows for a lot of flexibility. It also makes it easy for us to leave revisions in beta/trunk while merging others to release/trunk if some revisions did not pass tests in beta.
There's no one-size-fits-all answer for the subversion convention question IMHO.
It really depends on the dynamics of the project and company using it. In a very fast-paced environment, when a release might happen as often as every few days, if you try to religiously tag and branch, you'll end up with an unmanageable repository. In such an environment, the branch-when-needed approach would create a much more maintainable environment.
Also - in my experience it is extremely easy, from a pure administrative standpoint, to switch between svn methodologies when you choose to.
The two approaches I've known to work best are the branch-when-needed, and the branch-each-task. These are, of course, sort of the exact opposite of one another. Like I said - it's all about the project dynamics.