Binding ports when running Docker images in Singularity

Question

I am currently working on a distributed graph processing platform which maintains an Akka cluster inside of docker containers and have recently been granted access to a large cluster to test this. Unfortunately, this cluster does not run docker, only singularity.

This did not initially seem an issue as singularity supports docker images, however, due to the nature of the Akka cluster, I have to past several environment variables and bind several ports. As an example, a 'Partition Manager' within the system would be run with the following command:

docker run -p $PM0Port:2551  --rm -e "HOST_IP=$IP" -e "HOST_PORT=$PM0Port" -v $entityLogs:/logs/entityLogs $Image partitionManager $PM0ID $NumberOfPartitions $ZooKeeper

From looking through the Singularity documentation I can see that I can create a 'Singularity' file and specify the environment variables, but there doesn't seem to be any documentation on binding custom ports. Nor does it explain how I could pass arguments to the default entrypoint (The project is compiled with 'sbt docker:publish' so I am not sure exactly where this would be to reassign it).

Even if this was the solution, as there are multiple actor types (and several instances of each) it appears specifying environment variables and ports in a document would require templating, creating the files at run time, and building an image for each individual actor.

I am sure I have completely missed a page somewhere which would nicely translate this docker command into the equivalent singularity, but I just can't find it.

Answer 1

There is no network isolation in Singularity, so there is no need to map any port. If the process inside the container binds to an IP:port, it will be immediately reachable on the host.