I have a Vagrant configuration that provisions a few docker containers.
I start the machine by "vagrant up", and then "vagrant halt" the machine, and remove the provisioning of these containers.
On "vagrant up" I see these containers starting up anyways. It seems like the provisioning from the last run persisted somehow. I can only assume that the provisioning model is persistent. Is it?
How does Vagrant arrange for these containers to start at boot? How do I stop this from happening?
I doubt it's Vagrant per se restarting the containers unless that was specifically built into your VM. It really depends on a lot of factors -- starting with the Docker restart policy -- but also could be a factor of how your Docker daemon is setup or how the "halt" event is handled by the VM host.
The Docker images and each container’s file system persists after Docker shuts down, so you could provide some cleanup script to remove them prior to shutting down as well as make sure to set the restart policy --restart=no (which should be the default). (You should be able to docker inspect -f "{{ .HostConfig.RestartPolicy }}" <container> to view current policy.)
Related
I have a kubernetes cluster setup at home on two bare metal machines.
I used kubespray to install both and it uses kubeadm behind the scenes.
The problem I encounter is that all containers within the cluster have a restartPolicy: no which makes my cluster break when I restart the main node.
I have to manually run "docker container start" for all containers in "kube-system" namespace to make it work after reboot.
Does anyone have an idea where the problem might be coming from ?
Docker provides restart policies to control whether your containers start automatically when they exit, or when Docker restarts. Here your containers have the restart policy - no which means this policy will never automatically start the container under any circumstance.
You need to change the restart policy to Always which restarts the container if it stops. If it is manually stopped, it is restarted only when Docker daemon restarts or the container itself is manually restarted.
You can change the restart policy of an existing container using docker update. Pass the name of the container to the command. You can find container names by running docker ps -a.
docker update --restart=always <CONTAINER NAME>
Restart policy details:
Keep the following in mind when using restart policies:
A restart policy only takes effect after a container starts successfully. In this case, starting successfully means that the container is up for at least 10 seconds and Docker has started monitoring it. This prevents a container which does not start at all from going into a restart loop.
If you manually stop a container, its restart policy is ignored until the Docker daemon restarts or the container is manually restarted. This is another attempt to prevent a restart loop.
I am answering my question:
It wasn't probably very clear but I was talking about the kube-system pods that manage the whole cluster and that should automatically start when the machine restarts.
It turns out those pods (ex: code-dns, kube-proxy, etc) have a restart policy of "no" intentionally and it is the kubelet service on the node that spins up the whole cluster when you restart your node.
https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet/
In my case kubelet could not start due to missing cri-dockerd process.
Check the issue I opened at kubespray:
Verifying the kubelet logs is done like so:
journalctl -u kubelet -f
I want to restart the docker container only when container crashed due to error. And don't want to restart the container if host reboots.
Which restart_policy will work for the above case?
Start containers automatically
on-failure[:max-retries]
Restart the container if it exits due to an error, which manifests as a non-zero exit code. Optionally, limit the number of times the Docker daemon attempts to restart the container using the :max-retries option.
docker run -d --restart on-failure[:max-retries] CONTAINER
UPDATE
A Docker host is a physical computer system or virtual machine running Linux. This can be your laptop, server or virtual machine in your data center, or computing resource provided by a cloud provider. The component on the host that does the work of building and running containers is the Docker Daemon.
Keep containers alive during daemon downtime
By default, when the Docker daemon terminates, it shuts down running containers. You can configure the daemon so that containers remain running if the daemon becomes unavailable. This functionality is called live restore. The live restore option helps reduce container downtime due to daemon crashes, planned outages, or upgrades.
Enable live restore
There are two ways to enable the live restore setting to keep containers alive when the daemon becomes unavailable. Only do one of the following.
Add the configuration to the daemon configuration file. On Linux, this defaults to /etc/docker/daemon.json. On Docker Desktop for Mac or Docker Desktop for Windows, select the Docker icon from the task bar, then click Preferences -> Daemon -> Advanced.
Use the following JSON to enable live-restore.
{
"live-restore": true
}
Restart the Docker daemon. On Linux, you can avoid a restart (and avoid any downtime for your containers) by reloading the Docker daemon. If you use systemd, then use the command systemctl reload docker. Otherwise, send a SIGHUP signal to the dockerd process.
If you prefer, you can start the dockerd process manually with the --live-restore flag. This approach is not recommended because it does not set up the environment that systemd or another process manager would use when starting the Docker process. This can cause unexpected behavior.
I'm having trouble with docker where docker ps won't return and is stuck.
I found that doinng docker service restart something like
sudo service docker restart (https://forums.docker.com/t/what-to-do-when-all-docker-commands-hang/28103/4)
However I'm worried if it will kill all the running containers? (I guess the service do provide service so that docker containers can run?)
In the default configuration, your assumption is correct: If the docker daemon is stopped, all running containers are shut down.. But, as outlined on the link, this behaviour can be changed on docker >= 1.12 by adding
{
"live-restore": true
}
to /etc/docker/daemon.json. Crux: the daemon must be restarted for this change to take effect. Please take note of the limitations of live reload, e.g. only patch version upgrades are supported, not major version upgrades.
Another possibility is to define a restart policy when starting a container. To do so, pass one of the following values as value for the command line argument --restart when starting the container via docker run:
no Do not automatically restart the container. (the default)
on-failure Restart the container if it exits due to an error, which manifests
as a non-zero exit code.
always Always restart the container if it stops. If it is manually stopped,
it is restarted only when Docker daemon restarts or the container
itself is manually restarted.
(See the second bullet listed in restart policy details)
unless-stopped Similar to always, except that when the container is stopped
(manually or otherwise), it is not restarted even after Docker
daemon restarts.
For your specific situation, this would mean that you could:
Restart all containers with --restart always (more on that further below)
Re-configure the docker daemon to allow for live reload
Restart the docker daemon (which is not yet configured for live reload, but will be after this restart)
This restart would shut down and then restart all your containers once. But from then on, you should be free to stop the docker daemon without your containers terminating.
Handling major version upgrades
As mentioned above, live reload cannot handle major version upgrades. For a major version upgrade, one has to tear down all running containers. With a restart policy of always, however, the containers will be restarted after the docker daemon is restarted after the upgrade.
I am new to docker containers but we have containers being deployed and due to some internal application network bugs the process running in the container hangs and the docker container is not terminated. While we debug this issue I would like a way to find all those containers and setup a cron job to periodically check and kill those relevant containers.
So how would I determine from "docker ps -a" which containers should be dropped and how would I go about it? Any ideas? We are eventually moving to kubernetes which will help with these issues.
Docker already have a command to cleanup the docker environment, you can use it manually or maybe setup a job to run the following command:
$ docker system prune
Remove all unused containers, networks, images (both dangling and
unreferenced), and optionally, volumes.
refer to the documentation for more details on advanced usage.
I am running a docker container which contains a node server. I want to attach to the container, kill the running server, and restart it (for development). However, when I kill the node server it kills the entire container (presumably because I am killing the process the container was started with).
Is this possible? This answer helped, but it doesn't explain how to kill the container's default process without killing the container (if possible).
If what I am trying to do isn't possible, what is the best way around this problem? Adding command: bash -c "while true; do echo 'Hit CTRL+C'; sleep 1; done" to each image in my docker-compose, as suggested in the comments of the linked answer, doesn't seem like the ideal solution, since it forces me to attach to my containers after they are up and run the command manually.
This is by design by Docker. Each container is supposed to be a stateless instance of a service. If that service is interrupted, the container is destroyed. If that service is requested/started, it is created. If you're using an orchestration platform like k8s, swarm, mesos, cattle, etc at least.
There are applications that exist to represent PID 1 rather than the service itself. But this goes against the design philosophy of microservices and containers. Here is an example of an init system that can run as PID 1 instead and allow you to kill and spawn processes within your container at will: https://github.com/Yelp/dumb-init
Why do you want to reboot the node server? To apply changes from a config file or something? If so, you're looking for a solution in the wrong direction. You should instead define a persistent volume so that when the container respawns the service would reread said config file.
https://docs.docker.com/engine/admin/volumes/volumes/
If you need to restart the process that's running the container, then simply run a:
docker restart $container_name_or_id
Exec'ing into a container shouldn't be needed for normal operations, consider that a debugging tool.
Rather than changing the script that gets run to automatically restart, I'd move that out to the docker engine so it's visible if your container is crashing:
docker run --restart=unless-stopped ...
When a container is run with the above option, docker will restart it for you, unless you intentionally run a docker stop on the container.
As for why killing pid 1 in the container shuts it down, it's the same as killing pid 1 on a linux server. If you kill init/systemd, the box will go down. Inside the namespace of the container, similar rules apply and cannot be changed.