Run commands on docker swarm services regardless of which node it's on.

docker-service-exec

#!/bin/bash

# Run docker exec on service tasks on any host in a docker swarm.
#
# The first argument must be the service name all subsequent arguments are
# passed to that service task.
#
# The script looks for a docker context named ``node.<node hostname>``. If it
# doesn't exist the script will create a context by that name set to connect
# over ssh with the current local user as the username and the node name as the
# host. If the hostname belongs to the local node the ``default`` profile is
# copied to the required name.
#
# To override the automatically created docker context replace the context with
# an appropriately configured one with the same name.
#
# Author: haxwithaxe
# Copyright: haxwithaxe 2023
# License: GPLv3

set -e

SSH_PORT=${SSH_PORT:-22}
REMOTE_USER=${REMOTE_USER:-$(whoami)}


ensure_context() {
	local node_host=$1
	local user=${2:-$REMOTE_USER}
	local ssh_port=${3:-$SSH_PORT}
	if ! (docker context ls --format '{{ .Name }}' | grep -q node.$node_host); then
		if [[ "$(hostname --short)" == "$node_host" ]] || [[ "$(hostname --fqdn)" == "$node_host" ]]; then
			docker context create --from default node.$node_host
		else
			docker context create node.$node_host --docker "host=ssh://${user}@${node_host}:${ssh_port}"
		fi
	fi
}

main() {
	local service_name=$1
	shift
	docker context use default >/dev/null 2>&1
	local task_id=$(docker service ps --filter 'desired-state=running' $service_name -q)
	local node_id=$(docker inspect --format '{{ .NodeID }}' $task_id)
	local container_id=$(docker inspect --format '{{ .Status.ContainerStatus.ContainerID }}' $task_id)
	local node_host=$(docker node inspect --format '{{ .Description.Hostname }}' $node_id)
	ensure_context $node_host >/dev/null 2>&1
	docker context use node.$node_host >/dev/null
	local return_code=0
	docker exec -it $container_id "$@" || return_code=$?
	docker context use default >/dev/null 2>&1
	exit $return_code
}

main "$@"