I've made a (docker) container for ddclient.
The problem is that I'm having problems in running that service in the foreground so that the docker container keeps running.
I've managed to keep the docker running by adding a bashat the end of the script but this is hackish, since the actual process it should be whatching is the ddclient.
Another way I found was to tail -f the log file, but if the service stops, the container will keep running instead of stoping.
Q: So is there any (easy) way to keep a service running in the foreground?
The problem with the process (any process) running in a container is signal management: you need to make sure the SIGKILL and other signals are properly communicated to the right process(es) in order to successfully stop/remove a container (and not leave zombie processes: see "PID 1 zombie reaping issue")
One option is at least to make your service at least write in a log file
ENTRYPOINT ["/bin/sh" "-c" ]
CMD yourProcess > log
That should keep it in foreground, as suggested in "How do I bring a daemon process to foreground?".
For a service, try and use as a base image phusion/baseimage-docker which manages other services properly.
Related
I have the following script:
whie true
do
#code
sleep 60
done
I then wanted to create a service to start the machine and launch this script as service:
created my.service at /etc/systemd/system/my.service
[Unit]
Description=my Script
[Service]
Type=forking
ExecStart=/bin/script.sh
[Install]
WantedBy=multi-user.target
problem occurs when i systemctl start my.service
it goes to while true loop and hang in there, how can i run this service and make it run in the background ?
According to systemd specification at link. Type=forking is not exactly correct kind of start-up in your case
If set to forking, it is expected that the process configured with
ExecStart= will call fork() as part of its start-up. The parent
process is expected to exit when start-up is complete and all
communication channels are set up. The child continues to run as the
main service process, and the service manager will consider the unit
started when the parent process exits. This is the behavior of
traditional UNIX services. If this setting is used, it is recommended
to also use the PIDFile= option, so that systemd can reliably identify
the main process of the service. systemd will proceed with starting
follow-up units as soon as the parent process exits.
The Type=simple can be correct one. You can try with it
If set to simple (the default if ExecStart= is specified but neither
Type= nor BusName= are), the service manager will consider the unit
started immediately after the main service process has been forked
off. It is expected that the process configured with ExecStart= is the
main process of the service. In this mode, if the process offers
functionality to other processes on the system, its communication
channels should be installed before the service is started up (e.g.
sockets set up by systemd, via socket activation), as the service
manager will immediately proceed starting follow-up units, right after
creating the main service process, and before executing the service's
binary. Note that this means systemctl start command lines for simple
services will report success even if the service's binary cannot be
invoked successfully (for example because the selected User= doesn't
exist, or the service binary is missing).
If the application fails in the docker container you would not be able to troubleshoot what happened. Please propose a solution to that
docker ps -a
This will list all the containers including those who have already existed (for whatever reason)
Then you can copy the process id of the container of your interest and:
docker logs <pid of container that has failed>
Another interesting command is:
docker inspect <pid of container that has failed>
It returns a big json - you can check some sections there, like memory settings, "State" (if the process was OOM killed and so forth)
I am trying to run a Docker image on amazon ECS. I am using a command that starts a shell script to boot up the program:
CMD ["sh","-c", "app/bin/app start; bash"]
in order to start it because for some reason when I run the app (elixir/phoenix app) in the background it was crashing immediately but if I run it in the foreground it is fine. If I run it this way locally, everything works fine but when I try to run it in my cluster, it shuts down. Please help!!
Docker was supposed to keep track of your running foreground process, if the process stop, the container stop. The reason your container work when you use command with "bash" because bash wasn't stop.
I guess you use she'll script to start an application that serve in background like nginx or a daemon. So try to find an option that make the app running foreground will keep your container alive. I.e nginx has an option while starting "daemon off"
for some reason when I run the app (elixir/phoenix app) in the background it was crashing immediately
So you have a corrupted application and you are looking for a kludge to make it looking like it somewhat works. This is not a reliable approach at all.
Instead you should:
make it working in background
use systemctl or upstart to manage restarts of Erlang VM on crashes
Please note that it matters where you have your application compiled. It must be the exactly same architecture/container as the production one, with same Erlang, Elixir, OS versions, otherwise nobody guarantees it will be robust or even working.
I am using an image from docker hub and it uses cron to perform some actions after some interval. I have registered and pushed it as described in documentation as a worker process (not a web). It also requires several environment variables.
I've run it from command line, e.g. docker run -t -e E_VAR1=VAL1 registry.heroku.com/image_name/worker and it worked for few days, then suddenly stopped and I had to run the command again.
Questions:
Is this a correct way to run a docker (as worker process) in Heroku?
Why might it stop running after few days? Is there any logs to check?
Is there a way to restart the process automatically?
How properly set environment variables for the docker in Heroku?
Thanks!
If you want to have this run in the background, you should use the -d flag to disconnect stdin and stdout, and not -t.
To check logs, user docker logs [container name or id]. You can find out the container's name and id using docker ps -a. That should give you an idea as to why the container stopped.
To have the container restart automatically add the --restart always flag when you run it. Alternatively, use --restart on-failure to only restart when it exited with a nonzero exit code.
The way you set environment variables seems fine.
I have a build job on jenkins that is building my project and after it is done, it opens an ssh shell script on a remote server and transfers files and then stop and starts a daemon.
When I stop and start the daemon from the command line on a RHEL server, it executes just fine. When the job executes in jenkins, there are no errors.
The daemon stops fine and it starts fine. But shortly after starting, the daemon dies suddenly.
sudo service daemonName stop
# transfer files.
sudo service daemonName start
I'm sure that the problem isn't pathing
Does anyone know what could be special about the way Jenkins is executing the ssh shell script that would cause the daemon start to not fully complete?
The problem:
When executing a build through jenkins, the command to start the daemon process was clearly successfully executing, yet after the build job was done, the daemon would suddenly quit.
The solution:
I thought for this whole time that it was jenkins killing the daemon. So I tried many different incarnations and permutations of disabling the ProcessTree module that goes through and cleans up zombie child processes. I tried fooling it by resetting the BUILD_ID environment variable. Nothing worked.
Thanks to this thread I found out that that solution only works for child processes executed on the BUILD machine. I.E. not applicable to my problem.
More searching led me here: Run a persistent process via ssh
The solution? Nohup.
So now the build successfully restarts the daemon by executing the following:
sudo nohup service daemonname start
Jenkins watches for processes spawned by the job and kill them to avoid zombie processes.
See https://wiki.jenkins-ci.org/display/JENKINS/ProcessTreeKiller
The workaround is to override the BUILD_ID environment variable:
BUILD_ID=dontKillMe