understanding why podman-compose does things differently than podman itself

[spi43984]

This is not a bug report but an attempt to understand podman-compose better.

From some experiments I understand that podman itself

• supports pods with own namespaces, i. e. containers inside one pod can talk via the loopback interface
• creates an infra container inside a pod to keep the pod and its resources up and running

From what I see, podman-compose does that differently:

• pods don't contain an infra container
• pods get their own network assigned and every container gets an own IP address

I can get podman-compse to create an infra container as well by setting --pod-args='--infra=true --share=""' (can I set this in the compose.yml as well? Otherwise I need to change the systemd unit file as well). I can bind different container (services) to the same IP address by setting network_mode: "service:<servicename>" in the compose.yml file. I understand that in case I need to bind different services to the same port numbers I need different IP addresses and can't work with just one loopback address (but I still could use different loopback addresses in that case).

I'd like to understand what podman-compose all does differently than podman and why it does so - what are the benefits and maybe issues?

[muayyad-alsadi]

because this is what users who have existing yaml expect
for example https://github.com/containers/podman-compose/blob/devel/examples/awx3/docker-compose.yml

version: '3'
services:
# ...
  awx_web:
    image: "ansible/awx_web:3.0.1"
    hostname: awxweb
# ...

here this contain need to set a different hostname than the rest of the pod.

image two mysql servers one master and one slave on same pod, they need to open same port
which can't be done if they both are localhost

long long ago (when rootless containers did not have inter-container networking) we used to put all containers in a pod and make them talk via localhost

now rootless inter-container communication is feasible, so we moved to be more aligned with the SPEC
so we give our users what they expect without sacrificing the rootless daemon-less principles of podman

[muayyad-alsadi]

--pod-args='--infra=true --share=""' (can I set this in the compose.yml as well?

because starting the pod created with infra=true will report degraded unhealthy pod (because no one starts the infra, it will have let's say 4 containers only 3 of them running)

maybe this was a bug that is solved in podman v4 let me double check

UPDATE: here is the context

containers/podman#15048