How to avoid redundancy and time loss when re-building images during development? - deployment

Question

As a Vagrant user, when trying Docker I noticed one significant difference between development workflow with Vagrant and with Docker - with Docker I need to rebuild my image every time from scratch, even if I made minor changes in code.
This is major problem for me, because the process of image rebuilding oftenly very redundant and time consuming.
Perhaps there are some smart workflows with Docker already invented, if so, what are they?

Answer 1

I filed a feature-request for the vagrant-cachier plugin for saving docker build data and attached a bash workaround for that process. If it's okay for you to hack yourself around you can implement the scripts in vagrant.
caching docker build data with vagrant
Note that this procedure needs the vagrant-cachier plugin to be installed and has to save and load +300MB files from disk if they are new to the machine. Thus it's really slow if you have dockerfiles with just 1-5 lines of code but it's fast if you have dockerfiles with a lot of LOCs or images that have to be downloaded from the net.
Also note that this approach saves every intermediate building step. So if you are building an image and change a line in the middle of a dockerfile and build again the docker build process will get all cached intermediate containers till the changed line.
Using baseimages is still the preferred way but you can combine both procedures.
Feel free to post improvements and subscribe so fgrehm will maybe implement this in his plugin natively.

Answer 2

As Mark O'Connor suggested, one of the tips may be building a base image to your container(s). This image should have the dependencies, package installation, downloads... or any other consuming activity. This base image should be supposed to be built less frequently than the other one(s). In a similar way, if the final states of the execution of each step of your dockerfile doesn't change, Docker don't build this layer again. Thus, you can trying execute the commands than may change this state almost every run (e.g.: apt-get update) as later as you can, so docker don't have to rebuild the steps before. And also you can try to edit your dockerfiles in the later steps better than in the first.
Another option if you compile/download something inside the container is to have it downloaded or compiled in a host folder, and attach it to the container using -v or --volume option in docker run.
Finally there is other approaches to this issue as the one used by chef with knife container. In this approach you build the container using chef cookbooks, and each time you build it (because you have edited your cookbooks...) these changes are applied as a new docker layer (AUFS layer) and you don't have to repeat all the process. I didn't recommend this solution unless you have experience with Chef and you have cookbooks to manage your software. You should work harder to get it working and if you want Chef only to manage docker containers I think it doesn't worth it (although chef is a great option to manage infrastructures).
To automate the building process in case you have several images dependents itself, you can have a bash script that helps you with that task (credits to smola#github):
#!/bin/bash
IMAGES="${IMAGES:-stratio/base:test stratio/mesos:test stratio/spark-mesos:test stratio/ingestion:test}"
LATEST_TAG="${LATEST_TAG:-test}"
for image in $IMAGES ; do
USER=${image/\/*/}
aux=${image/*\//}
NAME=${aux/:*/}
TAG=${aux/*:/}
DIR=${NAME}/${TAG}
pushd $DIR
docker build --tag=${USER}/${NAME}:${TAG} .
if [[ $TAG = $LATEST_TAG ]] ; then
docker tag ${USER}/${NAME}:${TAG} ${USER}/${NAME}:latest
fi
popd
done

Answer 3

There are a couple of tricks that might better your workflow (very web-focused)
Docker caching
Always make sure you are adding your source to your Docker image in Dockerfile at the very end.
Example;
COPY data/package.json /data/
RUN cd /data && npm install
COPY data/ /data
This will make sure you get optimal caching when building the image, and that Docker doesn't have to rebuild the npm packages when you are changing your source.
Also, make sure you don't have a base-image that adds folders/files that are often changed (like base images doing COPY . /data/
fig mount
Use fig (or another tool), and mount your source directory when developing. This way, you can develop with instant changes and still use the current version of your code when building the image.
development server
You can start your developer web-server when you are developing, and nginx when not (if you are developing an www app, but same idea applies to other apps).
Example, in your startup script, do something like:
if [[ $DEBUG ]]; then
/usr/bin/supervisorctl start gulp
else
/usr/bin/supervisorctl start nginx
fi
And have autostart=false in your supervisord.conf files.
auto-refresh app
If you are developing a web-app, use tools like gulp and eg gulp-connect, if you are developing a python/django app, use the runserver utility. Both reloads the server when detecting changes in the files.
If you are using the if [[ $DEBUG ]] ... trick, make them listen on the same port as your normal instance (nginx). That way, you can have 1 configuration for your reverse proxy, ie, just send the traffic to example www:8080, it will hit your web-page both in production and if you are developing.

Answer 4

Create a based image that holds the bulk of your application's dependencies. This will significantly reduce your docker build times.