Compatibility mode

[shin-]

Using the --compatibility CLI flag, v3 files can be converted to their v2 equivalent, with deploy options translated when possible. --compatibility can be used with all commands.

The conversion is a "best effort" attempt and shouldn't be relied on for production deployments.

Fixes #4513

[shin-]

cc @mefyl @vdemeester for review 👓

[thaJeztah]

But doesn’t the V3 format already support memory and cpu limits? ie;

deploy:
      resources:
        limits:
          cpus: '0.50'
          memory: 50M
        reservations:
          cpus: '0.25'
          memory: 20M

[thaJeztah]

Oh; they were ignored by docker compose? Sorry, missed that

[shin-]

@thaJeztah Yes, the point here is to have a way to account for them in Compose as well. It's behind a flag because we can't really guarantee the behavior will match exactly what you would see with stack deploy. Does that make sense?

[dnephin]

Would it make sense make this an option on docker-compose config for converting a config from v3 to v2? That way you could inspect the changes to have some idea of what you're running.

[shin-]

@dnephin it works with config as well - it outputs a valid 2.3 file.

[thaJeztah]

It's behind a flag because we can't really guarantee the behavior will match exactly what you would see with stack deploy. Does that make sense?

Wondering; things like configs and secrets already have a different implementation in docker-compose; if we document that there are differences, would it make sense to enable it by default (possibly an option to disable it)?

[shin-]

I want to say no - the secrets emulation is super confusing to users as it is already (see feedback in #4994 for example). I think having users opt into the feature gives us a chance to setup expectations a little better.

[thaJeztah]

Ah, yes, then 👍 on the flag

[thiagolsfortunato]

When I executed docker-compose --compatibility config` return this message:

WARNING: The following deploy sub-keys are not supported in compatibility mode and have been ignored: resources.reservations.cpus

deploy:
      resources:
        limits:
          memory: 1G
          cpus: '1'
        reservations:
          memory: 512M
          cpus: '0.50'

Why flag --compatibility does not support resources.reservations.cpus and resources.limits.cpus as memory ?!

[thaJeztah]

Why flag --compatibility does not support resources.reservations.cpus and resources.limits.cpus equals memory ?!

Those options are scheduling options for swarm-mode services (i.e., they don't actually reserve the resources, only make swarm take those into account when scheduling containers on a node).

Docker Compose doesn't work with swarm mode (it deploys local containers), so there's no orchestrator to take those limits into account

[thiagolsfortunato]

For not swarm-mode, how can I manager memory and cpu resources deploying local containers?

[thaJeztah]

Using the feature described here; the warning that's printed is about cpu reservation;

Using this compose file:

version: '3.5'
services:
  web:
    image: nginx:alpine
    deploy:
      resources:
        limits:
          cpus: '0.50'
          memory: 50M

docker-compose --compatibility up -d
WARNING: The following deploy sub-keys are not supported in compatibility mode and have been ignored: resources.reservations.cpus
Creating network "compat_default" with the default driver
Creating compat_web_1 ... done

docker inspect compat_web_1

...
    "Memory": 52428800,
    "NanoCpus": 500000000,
...

[thaJeztah]

@shin- I just noticed this; this part isn't correct, because --memory-reservation (although named similar) is something very different than --reserve-memory on docker service; see moby/moby#14579

[ZacharyBacon]

https://blog.csdn.net/ZacharyBacon/article/details/121739675 为何不通过cgroup限制资源，现在只是支持swarm模式下，如果是非swarm下，可以通过挂载cgroup的文件来限制容器的资源。感兴趣的话，可以看下我写的这篇文章。

[lordraiden]

So now "limits" cpu/memory can be used with compatibility mode in a v3 file
But "cpu_shares", "cpu_quota", "cpuset", "mem_limit" can not be used unless you use a v2 file
right?

[thaJeztah]

@lordraiden this is a 6 year old pull request; docker compose v2 now uses the compose-specification file format which does not use a version, and unifies the v2 and v3 features; docs are located here; https://docs.docker.com/compose/compose-file/