execute a command within docker swarm service

Question

1. Initialize swarm mode:

   root@ip-172-31-44-207:/home/ubuntu# docker swarm init --advertise-addr 172.31.44.207  Swarm initialized: current node (4mj61oxcc8ulbwd7zedxnz6ce) is now a manager.  To add a worker to this swarm, run the following command: 

2. Join the second node:

   docker swarm join \ --token SWMTKN-1-4xvddif3wf8tpzcg23tem3zlncth8460srbm7qtyx5qk3ton55-6g05kuek1jhs170d8fub83vs5 \ 172.31.44.207:2377 

To add a manager to this swarm, run 'docker swarm join-token manager' and follow the instructions.

# start 2 services docker service create continuumio/miniconda3   docker service create --name redis redis:3.0.6   root@ip-172-31-44-207:/home/ubuntu# docker service ls ID            NAME        REPLICAS  IMAGE                   COMMAND 2yc1xjmita67  miniconda3  0/1       continuumio/miniconda3 c3ptcf2q9zv2  redis       1/1       redis:3.0.6 

As shown above, redis has it's replica while miniconda does not seem to be replicated.

I do usually log-in to miniconda container to type these commands:

/opt/conda/bin/conda install jupyter -y --quiet && mkdir /opt/notebooks && /opt/conda/bin/jupyter notebook --notebook-dir=/opt/notebooks --ip='*' --port=8888 --no-browser 

The problem is that docker exec -it XXX bash command does not work with swarm mode.

Answer 1

You can execute commands by filtering container name without needing to pass the entire swarm container hash, just by the service name. Like this:

docker exec $(docker ps -q -f name=servicename) ls

Answer 2

There is one liner for accessing corresponding instance of the service for localhost:

docker exec -ti stack_myservice.1.$(docker service ps -f 'name=stack_myservice.1' stack_myservice -q --no-trunc | head -n1) /bin/bash 

It is tested on PowerShell, but bash should be the same. The oneliner accesses the first instance, but replace '1' with the number of the instance you want to access in two places to get other one.

More complex example is for distributed case:

#! /bin/bash  set -e  exec_task=$1 exec_instance=$2  strindex() {    x="${1%%$2*}"   [[ "$x" = "$1" ]] && echo -1 || echo "${#x}" }  parse_node() {   read title   id_start=0   name_start=`strindex "$title" NAME`   image_start=`strindex "$title" IMAGE`   node_start=`strindex "$title" NODE`   dstate_start=`strindex "$title" DESIRED`   id_length=name_start   name_length=`expr $image_start - $name_start`   node_length=`expr $dstate_start - $node_start`    read line   id=${line:$id_start:$id_length}   name=${line:$name_start:$name_length}   name=$(echo $name)   node=${line:$node_start:$node_length}   echo $name.$id   echo $node }  if true; then     read fn     docker_fullname=$fn    read nn    docker_node=$nn  fi < <( docker service ps -f name=$exec_task.$exec_instance --no-trunc -f desired-state=running $exec_task | parse_node )  echo "Executing in $docker_node $docker_fullname"   eval `docker-machine env $docker_node`  docker exec -ti $docker_fullname /bin/bash 

This script could be used later as:

swarm_bash stack_task 1 

It just execute bash on required node.