Docker cheat sheet
While developing a docker backend urcap it is possible that something goes wrong, and you need to debug the container. This page will give a few tips for debugging a docker container.
The following section will go over a few common steps to debug containers like
How to ... COMMAND
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Enter a container with the terminal docker exec -it [container_id] bash
Run specific command inside a container docker exec [container_id] [command]
Show all running containers docker ps
Show all running and exited containers docker ps -a
Get log from container docker logs [container_id]
Get continuous log from running container docker logs -f [container_id]
Q: I want to check if my container is running
When you have installed your urcap (following install), it is possible to verify that the container is running by using the command
docker ps
This will show you a view similar to
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
363e4c9ecff1 ur/falcon-runtime:8.5.4 "run-docker.sh /bin/…" 1 minute ago Up 5 seconds 0.0.0.0:80->80/tcp, :::80->80/tcp, 2375-2376/tcp ursim-polyscopex-runtime-1
This shows that a container with the id: 363e4c9ecff1 is the simulator. Your backend urcap should be installed
inside this container. So now you can enter the container and then do the docker ps
docker exec -it 363e4c9ecff1 bash
This opens the container in your terminal which you can exit it again by writing: exit.
Now that you are inside the PolyScope X simulator you can write the docker ps command:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
c74eeddf729e universal-robots_ur-cloud_ur-cloud:latest "gunicorn '-b :5000'…" 55 seconds ago Up 54 seconds 5000/tcp universal-robots_ur-cloud_ur-cloud
66f0933c5126 universal-robots_ros2-web-bridge_ros2-web-bridge:latest "/venv/bin/python3 m…" 57 seconds ago Up 57 seconds universal-robots_ros2-web-bridge_ros2-web-bridge
3521cba2fbe0 universal-robots_java-backend_java-backend-prod:latest "/usr/local/s2i/run" About a minute ago Up About a minute 8080/tcp, 8443/tcp, 127.0.0.1:5005->5005/tcp, 30015/tcp universal-robots_java-backend_java-backend
35606367cf13 universal-robots_web-frontend-app_web-recording-engine:latest "flask run --host 0.…" About a minute ago Up About a minute 52762/tcp universal-robots_web-frontend-app_web-recording-engine
87285506c629 ur/web-bootstrapper:latest "./bootstrapper_entr…" About a minute ago Up About a minute root-web-bootstrapper-1
bedbaaf4ec26 docker.urrd.dk/urservice:13.0.12 "./urservice" About a minute ago Up About a minute (healthy) 8181/tcp root-urservice-1
5df34bbc465b docker.urrd.dk/tool/controller-artifact:67.8.0 "/entrypoint --robot…" About a minute ago Up About a minute 0.0.0.0:30001-30002->30001-30002/tcp, 0.0.0.0:30004->30004/tcp, 0.0.0.0:30011-30013->30011-30013/tcp, 0.0.0.0:30020->30020/tcp root-urcontrol-primary-1
697d887cc958 docker.urrd.dk/nginx:1.22.1 "/docker-entrypoint.…" About a minute ago Up About a minute 0.0.0.0:80->80/tcp root-nginx-1
6835292e2c78 docker.urrd.dk/ur/ur-auth-in-docker:1.3.0 "java -jar -XX:+UseS…" About a minute ago Up About a minute 0.0.0.0:28999->28999/tcp root-ur-auth-1
363e4c9ecff1 my_first_sleeping_urcap:1.0.0 "sleep 3600" About 2 minute ago Up About a minute
This shows all the containers that are running - and have not exited - in the PolyScope X simulator.
Shortcut
It is possible to skip entering the PolyScope X simulator and execute the docker ps command by combining with the
docker exec command. We leverage the knowledge that per default the PolyScope X simulator is started with the name
ursim-polyscope-runtime-1 which we can use instead of the container id for the docker exec.
docker exec ursim-polyscopex-runtime-1 docker ps
Q: I am not able to see my container
If you installed the urcap, but it doesn’t show up it might be because it exited for some unknown reason. In that case
you can add -a to docker ps like docker ps -a. This will print the containers also with the exit status.
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
...
363e4c9ecff1 my_first_sleeping_urcap:1.0.0 "sleep 1234" About a minute ago Exited (137) 36 seconds ago
Q: Why did my container exit?
With the above command we can try and get the logs from the container. To do that we want to use the
docker logs [container_id] command. But inside the container where the urcap is installed.
docker exec ursim-polyscope-runtime-1 docker logs 363e4c9ecff1
Which will then print out the logs from the container before it shuts down. Now it is then possible to see if there was anything out of the ordinary in the logs. If you are unable to find any apparent reason for the shutdown it might be necessary to add debug statements which can be followed in the log and re-run with the container.
Shortcut
You might have noticed that instead of a [container_id] we have been using ursim-polyscope-runtime-1, when
referring to the simulator. Likewise, you can do the same when referring to your installed URCap. So you can
get the logs from the URCap with
docker exec ursim-polyscope-runtime-1 docker logs [vendor_id]/[urcap_id]/[artefact_id]
Which is the tags that you have defined when you created the URCap. Since the [container_id] can change when
making changes to the URCap and re-installing it, using the [vendor_id]/[urcap_id]/[artefact_id] could be user
while developing.
Q: I added my debug statements and want to follow the logs while running
To be able to follow the logs while a container is running the optional follow flag -f can be used with
docker logs for a combined docker logs -f [container_id]. So after adding debug statements to the URCap
and installing it you can now write
docker exec ursim-polyscope-runtime-1 docker logs -f 363e4c9ecff1
Which will then continuously print the logs from the container until you do a CTRL+C to stop running the command.
As an example the logs could look something like the following where the container prints out the first available
time that it starts up. Since the purpose of this container is to sleep, it also prints out that it is about to do
that. And then every 10 seconds. Which we notice it does so twice before it shuts down.
ursim-polyscopex-runtime-1 | my_first_sleeping_urcap-1 | 2023/12/24 18:00:00 Debug: Just entering my script
ursim-polyscopex-runtime-1 | my_first_sleeping_urcap-1 | 2023/12/24 18:00:01 Debug: About to call the sleep command
ursim-polyscopex-runtime-1 | my_first_sleeping_urcap-1 | 2023/12/24 18:00:12 Debug: I have now slept for 10 seconds
ursim-polyscopex-runtime-1 | my_first_sleeping_urcap-1 | 2023/12/24 18:00:22 Debug: I have now slept for 10 seconds
ursim-polyscopex-runtime-1 | my_first_sleeping_urcap-1 | 2023/12/24 18:00:28 Called exit with status 137