I'm using Docker to run a java REST service in a container. If I were outside of a container then I might use a process manager/supervisor to ensures that the java service restarts if it encounters a strange one-off error. I see some posts about using supervisord inside of containers but it seems like they're focused mostly on running multiple services, rather than just keeping one up.
What is the common way of managing services that run in containers? Should I just be using some built in Docker stuff on the container itself rather than trying to include a process manager?
You should not use a process supervisor inside your Docker container for a single-service container. Using a process supervisor effectively hides the health of your service, making it more difficult to detect when you have a problem.
You should rely on your container orchestration layer (which may be Docker itself, or a higher level tool like Docker Swarm or Kubernetes) to restart the container if the service fails.
With Docker (or Docker Swarm), this means setting a restart policy on the container.
I' have the following docker setup:
Ubuntu server
-> running Jenkins (started with docker-compose)
-> running a pipeline which starts a node-alpine image
-> which then calls a new docker-compose up (needed for tests)
If I call docker ps from the node-alpine container, I see all the containers from the ubuntu server. I would have expected to only see the newly started containers.
Is this an indication that my setup is flawed? Or just the way docker works?
That's just the way Docker works. There's no such thing as a hierarchy of containers.
Typically with setups like this you give an orchestrator (like Jenkins) access to the host's Docker socket. That means containers launched from Jenkins are indistinguishable from containers launched directly from the host, and it means that Jenkins can do anything with Docker that you could have done from the host.
Remember that access to the Docker socket means reading and modifying arbitrary files as root on the host, along with starting, stopping, deleting, and replacing other containers. In this setup you might re-evaluate how much you really need that lowest level container to start further containers, since it is a significant security exposure.
I see this in many docker apps that are somehow related hardly on networking, but I can't understand this
Got it.
https://jpetazzo.github.io/2015/09/03/do-not-use-docker-in-docker-for-ci/
Let’s take a step back here. Do you really want Docker-in-Docker? Or
do you just want to be able to run Docker (specifically: build, run,
sometimes push containers and images) from your CI system, while this
CI system itself is in a container?
I’m going to bet that most people want the latter. All you want is a
solution so that your CI system like Jenkins can start containers.
And the simplest way is to just expose the Docker socket to your CI
container, by bind-mounting it with the -v flag.
Simply put, when you start your CI container (Jenkins or other),
instead of hacking something together with Docker-in-Docker, start it
with:
docker run -v /var/run/docker.sock:/var/run/docker.sock
Now this
container will have access to the Docker socket, and will therefore be
able to start containers. Except that instead of starting “child”
containers, it will start “sibling” containers.
Can't seem to find recommended way to do this.
I have a vm host using unintuitive running a number of containers.
It is using an older version of docker and I want to update.
What are the steps to do this?
Stop containers.
Do update of docker version
Restart containers.
Trying to minimise downtime and don't have the option to bring up a new vm. Also vm contains volume data I don't want to lose
Depending on your distribution, run command to update docker.
e.g. on CentOS run yum update docker-engine
This will stop your containers, update docker and start containers which were configured to restart automatically (e.g. docker run --restart=always ...).
Please note that in case your container is configured to be removed automatically (docker run --rm ...) you will loose all data associated with the container unless you manage the data via volumes.
In case you use external service discovery tool, the port mapping of the exposed ports usually change so you should trigger an update of the ports in the external service discovery tool.
I'm running Jenkins inside a Docker container. I wonder if it's ok for the Jenkins container to also be a Docker host? What I'm thinking about is to start a new docker container for each integration test build from inside Jenkins (to start databases, message brokers etc). The containers should thus be shutdown after the integration tests are completed. Is there a reason to avoid running docker containers from inside another docker container in this way?
Running Docker inside Docker (a.k.a. dind), while possible, should be avoided, if at all possible. (Source provided below.) Instead, you want to set up a way for your main container to produce and communicate with sibling containers.
Jérôme Petazzoni — the author of the feature that made it possible for Docker to run inside a Docker container — actually wrote a blog post saying not to do it. The use case he describes matches the OP's exact use case of a CI Docker container that needs to run jobs inside other Docker containers.
Petazzoni lists two reasons why dind is troublesome:
It does not cooperate well with Linux Security Modules (LSM).
It creates a mismatch in file systems that creates problems for the containers created inside parent containers.
From that blog post, he describes the following alternative,
[The] simplest way is to just expose the Docker socket to your CI container, by bind-mounting it with the -v flag.
Simply put, when you start your CI container (Jenkins or other), instead of hacking something together with Docker-in-Docker, start it with:
docker run -v /var/run/docker.sock:/var/run/docker.sock ...
Now this container will have access to the Docker socket, and will therefore be able to start containers. Except that instead of starting "child" containers, it will start "sibling" containers.
I answered a similar question before on how to run a Docker container inside Docker.
To run docker inside docker is definitely possible. The main thing is that you run the outer container with extra privileges (starting with --privileged=true) and then install docker in that container.
Check this blog post for more info: Docker-in-Docker.
One potential use case for this is described in this entry. The blog describes how to build docker containers within a Jenkins docker container.
However, Docker inside Docker it is not the recommended approach to solve this type of problems. Instead, the recommended approach is to create "sibling" containers as described in this post
So, running Docker inside Docker was by many considered as a good type of solution for this type of problems. Now, the trend is to use "sibling" containers instead. See the answer by #predmijat on this page for more info.
It's OK to run Docker-in-Docker (DinD) and in fact Docker (the company) has an official DinD image for this.
The caveat however is that it requires a privileged container, which depending on your security needs may not be a viable alternative.
The alternative solution of running Docker using sibling containers (aka Docker-out-of-Docker or DooD) does not require a privileged container, but has a few drawbacks that stem from the fact that you are launching the container from within a context that is different from that one in which it's running (i.e., you launch the container from within a container, yet it's running at the host's level, not inside the container).
I wrote a blog describing the pros/cons of DinD vs DooD here.
Having said this, Nestybox (a startup I just founded) is working on a solution that runs true Docker-in-Docker securely (without using privileged containers). You can check it out at www.nestybox.com.
Yes, we can run docker in docker, we'll need to attach the unix socket /var/run/docker.sock on which the docker daemon listens by default as volume to the parent docker using -v /var/run/docker.sock:/var/run/docker.sock.
Sometimes, permissions issues may arise for docker daemon socket for which you can write sudo chmod 757 /var/run/docker.sock.
And also it would require to run the docker in privileged mode, so the commands would be:
sudo chmod 757 /var/run/docker.sock
docker run --privileged=true -v /var/run/docker.sock:/var/run/docker.sock -it ...
I was trying my best to run containers within containers just like you for the past few days. Wasted many hours. So far most of the people advise me to do stuff like using the docker's DIND image which is not applicable for my case, as I need the main container to be Ubuntu OS, or to run some privilege command and map the daemon socket into container. (Which never ever works for me)
The solution I found was to use Nestybox on my Ubuntu 20.04 system and it works best. Its also extremely simple to execute, provided your local system is ubuntu (which they support best), as the container runtime are specifically deigned for such application. It also has the most flexible options. The free edition of Nestybox is perhaps the best method as of Nov 2022. Highly recommends you to try it without bothering all the tedious setup other people suggest. They have many pre-constructed solutions to address such specific needs with a simple command line.
The Nestybox provide special runtime environment for newly created docker container, they also provides some ubuntu/common OS images with docker and systemd in built.
Their goal is to make the main container function exactly the same as a virtual machine securely. You can literally ssh into your ubuntu main container as well without the ability to access anything in the main machine. From your main container you may create all kinds of containers like a normal local system does. That systemd is very important for you to setup docker conveniently inside the container.
One simple common command to execute sysbox:
dock run --runtime=sysbox-runc -it any_image
If you think thats what you are looking for, you can find out more at their github:
https://github.com/nestybox/sysbox
Quicklink to instruction on how to deploy a simple sysbox runtime environment container: https://github.com/nestybox/sysbox/blob/master/docs/quickstart/README.md