[docs] Added description how to run task inside a docker container

Author: justonedev1

README.md

@@ -190,6 +190,7 @@ There are two ways of interacting with AliECS:
       * [Hashing to aggregate](/docs/metrics.md#hashing-to-aggregate)
       * [Sampling reservoir](/docs/metrics.md#sampling-reservoir)
   * [OCC API debugging with grpcc](/docs/using_grpcc_occ.md#occ-api-debugging-with-grpcc)
+  * [Running tasks inside docker](/docs/running_docker.md#running-task-inside-a-docker-container)
 
 * Resources
   * T. Mrnjavac et. al, [AliECS: A New Experiment Control System for the ALICE Experiment](https://doi.org/10.1051/epjconf/202429502027), CHEP23

docs/running_docker.md

@@ -0,0 +1,37 @@
+# Running task inside a docker container
+
+> **WARNING**: This method is not meant for the production use and is meant only as a POC to test docker images as a part of existing pipeline. Right now it was tested with outdated alma8-flp-node image running readout
+
+## How to
+
+As a first step we need to be sure that required host computer has installed `docker`. At the time of writing this document `docker` needs to be installed manually.
+
+In order to run task inside a docker image on the executor we can simply wrap the binary call into the docker image inside the [ControlWorkflow](https://github.com/AliceO2Group/ControlWorkflows) repository. For example in order to run readout we can modify `_plain_command` part of [`readout.yaml`](https://github.com/AliceO2Group/ControlWorkflows/blob/master/tasks/readout.yaml) by adding `docker run image command`. Obviously we need to have docker image that contains required binary with proper settings (creating one is outside of this document). A bit tricky part is that we need to manually (for now) specify all ENV variables with `-e` option in `docker run` call. Moreover we might need to add `--network=host` and `--ipc=host` to the call itself. Michal Tichak was able to run readout inside the alma8-flp-node as a part of workflow using following:
+
+```
+"/usr/bin/docker run --network=host --ipc=host -v /tmp:/tmp -e O2_DETECTOR={{ detector }} -e O2_PARTITION={{ environment_id }} -e OCC_CONTROL_PORT=31000 -e O2_SYSTEM=FLP -e O2_ROLE=mtichak-ostack gitlab-registry.cern.ch/aliceo2group/dockerfiles/alma8-flp-node:latest /opt/o2/bin/o2-readout-exe"
+```
+
+In order to figure out all of the ENV variables required one can take a look into the ECS gui environment details page and find task in question where all of the env variables are defined while running the binary outside of docker.
+
+## Tips and tricks
+
+Production systems run RHEL which doesn't install native `docker` by running `dnf install docker` but they are emulating the functionality by using `podman` which might behave different.
+
+In order to debug whether ECS is even starting the container we can use
+
+```
+docker ps -a
+```
+
+This will show all of the containers which were run/are runinng on the system under current user. However there is a catch: ECS is using user `flp` so in order to figure out which container was running under this user, we need to switch the user by
+
+```
+su - flp
+```
+
+You can show logs directly from docker itself by using:
+
+```
+docker logs [container-id|name]
+```