host pid mode in swarm mode.

[asleea88]

Problem description

Swarm mode doesn't support host pid mode with pid option?. as my testing It seems not and I couldn't find any information anywhere on that.

As I know, the document remarks some different support between docker-compose and swarm mode. however, when it comes to pid, there is no mention about that pid option is not supported in swarm mode. I want a container to share PID namespace with host OS in swarm mode to manage processes on manager node.

This un-support is on purpose?

Problem location

version: '3.4'
services:
    test:
        image: ubuntu:16.04
        command: tail -f /dev/null
        pid: host

$ docker stack deploy -c docker-compose.yml pid_share

$ docker ps 
CONTAINER ID        IMAGE                             COMMAND               CREATED             STATUS              PORTS               NAMES
8a2d4b439efa        asleea/simple_test:latest         "tail -f /dev/null"   2 hours ago         Up 2 hours                              test_test.qdma0yzo931ydcsuc6z5lef3n.w1h4vwox5o6lmt51ugt01w4a8

$ docker exec -it test_test.qdma0yzo931ydcsuc6z5lef3n.w1h4vwox5o6lmt51ugt01w4a8 top
top - 07:02:53 up  5:09,  0 users,  load average: 0.06, 0.04, 0.00
Tasks:   2 total,   1 running,   1 sleeping,   0 stopped,   0 zombie
%Cpu(s):  1.2 us,  0.3 sy,  0.0 ni, 98.5 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem :  8154208 total,  6221900 free,   691592 used,  1240716 buff/cache
KiB Swap:  8386556 total,  8386556 free,        0 used.  7052380 avail Mem 

   PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                                                                                                 
     5 root      20   0   36636   2988   2560 R   0.3  0.0   0:00.02 top                                                                                                                     
     1 root      20   0    4412    680    608 S   0.0  0.0   0:00.04 tail 

The top command show only processes in the container but host OS.

Project version(s) affected

docker 17.09.0-ce
docker-compose 1.17.0

[thaJeztah]

Correct --pid=host is not currently supported for Swarm services (see moby/moby#25303).

Opened docker/cli#768 to print a warning if this option is used

[mdlinville]

We document limitations about flags in the repo @thaJeztah posted. Thanks! Closing this one.

[thaJeztah]

Perhaps it still needs a mention in the compose file reference (haven't checked yet)

[odama626]

It seems like everything but the tasks is working in swarm, and looking into psutils it looks like exposing psutil.PROCFS_PATH through an environment variable or something could allow this to work?

giampaolo/psutil#1011 (comment)

[tomdaley92]

Perhaps it still needs a mention in the compose file reference (haven't checked yet)

I just stumbled upon this expected it to work in swarm mode. There is currently no mention of incompatibility with docker swarm in the compose docs.

[docker-robott]

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