Please excuse my ignorance. I don't know anything and am just trying to learn.
I've been thinking and it appears to me that spinning off more virtual machines on a single computer so you can run separate services on each VM instance only creates isolation between those services so that if one VM instance were crash, it wouldn't affect the others.
If the same service were installed on each of the VM's, then it also provides for availability.
But it does not help the scalability of your services because each VM on the same hardware must share the same limited hardware resources such as disk, memory, CPU, and network interface cards.
Am I thinking right? Sorry if this isn't the right forum to ask this sort of a question. If someplace else is more appropriate, please feel free to move it there.
Virtualization is a thing of the post. Now it's all about containerization. I would suggest you to look into Docker and specifically docker-compose
Try visiting https://www.docker.com, and also https://docs.docker.com/compose/gettingstarted/
Hope It helps.
Virtual Machines have the advantage that you can adjust the parameters of usage. You can change virtual hardware, memory, disk-space and CPU-usage.
This makes the VM scalable related to the needs.
And if the Host-Machine is getting to weak to serve the requirements you can move the VM on another Host-Machine.
If you want to run a server with maximum available resources it's better to do it without VM but with the best hardware you can get / pay because the VM adds an additional level to computing and is using resources too.
Related
The server will run singly on one instance of compute engine. What could limit it's serving capacity and how much load can a single instance (4 vCPUs and 15GB Memory) handle.
Note : I've already looked at Kubernetes and even load-balancing multiple instances but accessing the database from multiple clients is a little too complicated for me right now. So please keep in mind if you're going to suggest containerisation, that I'm a beginner.
Any and all advice is welcome. Thanks!
The serving capacity of the server depends on a number of factors, which includes the requests you receive from the clients, the additional applications running in it etc. For a 4 core CPU, as per this help center article, you will get a peak performance of 8Gb/s, which is good for a single instance. Since you are using a single parse server alone on the VM, it should work very well with the above-mentioned configuration.
A container is a tool for a developer. It contains all the dependencies and library which required to run/test a particular application in a container. The applications running in the container are easily portable.
There is this help center article which might give a precise idea of containers and its usage. While the Kubernetes Engine will help you to deploy/manage these containerized application.
I have my RHEL linux server(VM) running a 4core processor and 8GB ram running the below applications
- an Apache Karaf container
- an Apache tomcat server
- an ActiveMQ server
- and the mongod server(either primary of secondary).
Often I see that mongo consumes nearly 80% of cpu. Now I see that my cpu and memory is overshooting most of the time and this has caused me to doubt whether my hardware config is too low for running these many components.
Please let me know if it is ok to run mongo like this on a shared server..
The question is to broad and the answer depends on too many variables, but I'll try to give you overall sense of it.
Can you use all these services together on the same machine at a minimum load? - for sure. It's not clear where other shards reside though, but it will work either way. You didn't provide your HDD specs which is quite important for a DB server, but again it will work at a minimum load.
Can you use this setup under heavy load - not the best idea. Perhaps it's better to have separate servers handling these services.
Monitor overall server load like: CPU, memory, IO. Check mongo logs for slow queries. If your queries supposed to run fast and they don't, you'll need more hardware.
Nobody would be really able to tell you how much load a specific server configuration can handle. You need at least 512Mb RAM and 1 CPU to get going these days but very soon you hit the limits. It all depends on how many users you have, what kinds of queries they run and how much data they cover.
Can you run MongoDB along other applications on a single server? Well it would appear that if you are having memory issues or CPU issues in your current configuration then you will likely need to address something. But "Can You?", well if it is not going to affect you then of course you can.
Should you, do this? Most people would firmly agree that you should not, and that would also stand for most of the other applications you are running on the one machine.
There are various reasons, process isolation, resource allocation, security, and far too many for a short topic response to go into why you should not have this kind of configuration. And certainly where it becomes a problem you should be addressing the issue by seeking a new configuration.
For Mongo alone, most people would not think twice about running their SQL database on dedicated hardware. The choice for Mongo should likely be no different.
Have also suggested this be moved to ServerFault, as it is not a programming question suited to stack overflow.
I have a question regarding the dynamic zoning for resources assigned to Virtual machines, is there anyway to dynamically control the resources assigned for Virtual machines whatever is the hypervisor, I want to know what things needed to be considered if I am having different load time during the day so the VM should response to this variation at same time, if the customer asks for doubling the assigned resources for his/her VM there should something guarantees that the bandwidth or whatever the assigned resources will be doubled according to the request.
Can anybody explain to me which hypervisor implement this as my knowledge this is isn't possible in the current Opensource hypervisors xen, kvm, vbox,... etc, as I never worked with any commercial hypervisor before?
Thanks in advance
did you check about cgroups? I am not sure about guarantee, but they can help you to expand resources whenever you need them through resource controllers.
I see many deployments where IT groups run effectively nothing but a JVM application stack inside a VM (vmware, &c) instance.
I guess I consider the JVM to be a formal VM: what real benefit is it to run your Java application stack inside another VM?
Two JVM instances within the same (real or virtualized) machine wouldn't be completely isolated from each other: they couldn't both have sockets listening on the same well-known numbered port, they might interfere with each other if they both wrote in the same filesystem, and so on, and so forth.
Using OS-level VMs (vmware or whatever) does guarantee you as much isolation as you would have on physically separate systems, which is quite a different proposition.
It's an unfortunate terminology collision
Those are really two different terms that unfortunately use the same english words, but have only a rather abstract connection.
IBM used the term "virtual machine" first, so I guess we can't rename that one to "virtual server" or something.
Too bad "software framework" doesn't have VM in its initials. If you think of the JVM that way it will be obvious that you are really just running a framework in a VM, not a thing inside the same kind of thing...
So a real VM can casually give away super user shell accounts, ssh access, software installation privs, ....
what real benefit is it to run your Java application stack inside another VM?
By doing this, your JVM will run on virtualized hardware that you can modify and run in parallel of other virtual machines. This is a nice way to slice a big server into "shares" that you can allocate on demand.
(EDIT: I'm answering a comment from the OP directly in this answer)
I get what you're saying, but why would one not be able to do the very same thing as separate processes on the host OS?
I could mention that a guest can possibly run another OS but this is not the most important part. As pointed out in another answer, the biggest difference is that a virtual machine is isolated from other VMs, it's are real dedicated environment. The port stuff was a good example but I prefer to illustrate it this way: another process won't eat "your" CPU cycles. This is a very important difference, especially for IT teams that usually don't like to share resources. Instead, you can size a virtual machine exactly as needed, possibly dynamically, and bill IT teams for what they are really using. This is IMO what makes mutualisation of resources actually possible (and thus costs cutting).
Why does it help to know about virtualization from a programmer's perspective? Except testing and developing on several different platforms without the need of switching between operating systems is there a particular reason why virtualization is important for a programmer? Are there any details that must be kept in mind before developing on virtual instances?
I use it for testing our installer, because it is important to check whether the application will work on a clean installation of the operating system.
I used to do these tests by keeping a hard drive with a fresh operating system installation and making a copy of that disk for (almost) every new test run. This was very time consuming, and the virtual machine solution has saved me a lot of time. Note that this even allows you to do remote debugging as easily as when using two non-virtual machines.
Note: If you're interested, I'm using VirtualBox, which is a very good and free virtualization tool.
If you develop a driver or something very close to the hardware with a high risk to crash the machine, you will be glad to be working on a virtual machine.
Reverting to an old state is easier than to repair a damaged OS.
One of the main advantages is having your entire development environment as a single image file. I have a perfectly configured version of Windows Server, Visual Studio, ReSharper, etc. I can easily try a new version of something on a copy of this virtual machine without worrying about it causing problems.
I can also back up my entire dev environment to transfer it to another physical machine very easily. I've been through 3 machines in this office alone so that was a lifesaver in itself.
The only real trade-off I see is performance. You generally have to use less physical CPU cores than you actually have and less memory. With a sufficiently powerful machine this is not much of a problem though.
Edit: As nader said, I/O is obviously important for most projects as well. Although developing on a virtual machine does mean a fairly large I/O penalty compared with a native OS install, in practice I rarely find it to be a problem. The superior random access capabilities of SSDs are helping to mitigate this drawback as well.
Being able to completely reset the state of the system is very useful to debug applications which modify their environment - If the actions are repeated after a reset, and they're constrained to the sandbox environment of the VM, you are pretty much guaranteed to get the same result.
We have a large number of different versions / customer customisations of our software, and its not possible for 2 installs of our software to coexist on the same machine. Virtualisation allows us to replace the 50-60 physical machines that we need to maintain for testing and problem reproduction with 2-3 virtual servers - it takes around 10 miniutes to make a copy of a VHD template we have and create a new virtual machine, and as long as you allocate 1-2Gb of RAM the performance is comparable to that of a (slow) physical machine.
Virtual machines are also great for build machines.
Personally I do all of my development on my deskop machine for best performance, and remote debug into VMs. I dont run virtual machines on my desktop as it uses up too much RAM, we have dedicated virtual servers for that.
Good for developing, because you have same server configuration in virtual machine like on production server.
https://stackoverflow.com/questions/905926/developer-software-setup
From a user space application there should be no difference developing for a virtualised OS versus a normal OS. There may be some gotchas if your code makes explicit assumptions of the machines memory size and number of processors and believes what the hypervisor tells you.
I'm surprised no one has mentioned the ease of deployment. All you need to do is get the build down on the virtual O/S and then you can copy the image to as many new servers (running some kind of virtualization solution [like VMWare]) as you want, easily scaling your application.
Record the state of a bug in a program, and send it to the developer (along with the entire "machine").
Testing your code on various O.S, some of which you don't have.
Working in a more protected environment, making sure that the code doesn't harm your system -useful for understanding dangerous programs, like viruses, and developing security against it, for writing potentially wrong hard-drive programs, and anything that can have catastrophic effects on your system.
Easily Write your own O.S without the need to write on 'real' boot sectors, a potentially harmful act (Hope this is not new...).
Quickly use tools and programs not found on your own O.S.
Demonstrate a program at various times, by restoring a virtual machine,
quicker and less prone to failure, than trying to recreate the state at the minutes before the demo.
Less directly connected to programing, but surfing vie a virtual machine (for example to see documentation) has the added value that your own important system (and code) is less likely to be harmed by malicious programs.
From my experience in most cases the answer is typically "no" (When testing and targeting multiple platforms is removed) Both are huge reasons to be familiar with "desktop" VM solutions. Others have done an excellent job of listing rare exceptions like debugging kernel codes.
There are some quirks one must be aware of when running on a virtual machine. This is hardly an exhaustive list:
Loss of precsision or even time reversal in high resolution timers due to emulation of hardware resources (depends somewhat on the vm platform and operating system)
Virtual network interfaces ususally bridged. We've seen some extremely odd behavior in the host system with an application that sets up its own bridge between virtual interfaces -behavior which logically should not effect the host in one of the leading VM solutions.
Usage models - If your product has orwellian licensing codes or records state dependant behavior when interacting with remote systems you should account for what would happen if a system were "paused" and "restarted" or restarted from an earlier "state". Normally this kind of thing would be taken into account anyway in a robust implementation.
If you are developing in a virtual environment you will want to make sure you know what specifications were used to create the environment. If you have say a 4 Gig machine and create a virtual environment with 1 Gig you will want to make sure things in your development do not grow to a point that it overruns the memory. This will cause slight performance problems. I personally ran into this and it was a pretty tricky thing to track down. The scenario was that I was fixing a bug and testing it in a virtual environment. I did not setup the virtual environment by the way... The application took a performance hit because of all of the memory swapping that was taking place.
A very good use for a virtual environment is when you are developing applications that mess with the Windows Gina. It's much easier to reinstall a virtual environment than an entire PC....(been here done that too).
I do all of my development on a virtual XP instance under VMWare Fusion so that I can use a Mac for everything and still write .NET code ;-)
Sometimes they are necessary, because the platform you are programming doesn't support the standard developer environment. One such example is Sharepoint. As of Sharepoint 2007 you still need a server OS to install Sharepoint 2007, WSS, and the Visual Studio Sharepoint Extensions (VseWSS).
Thus for Sharepoint I have to use a Window Server VM to do my development work. As for Sharepoint 2010 they are supporting installations on Vista and 7 x64, but I will still use a VM, because I don't want to have Sharepoint on my main machine slowing everything down. Rather I want it in a VM where the services are on when needed and off when I don't without having to manually turn off/on each service. This in addition to the many great answers posted above.