In Docker Swarm mode, how can I restart a single global service? Is it even possible? I know you can scale replicated services to zero then back to 1+, but there doesn't appear to be any documentation on how to have the same effect with global services.
I am updating my SSL certificate so would like to just restart our reverse proxy instead of restarting our entire app (via restarting the docker service).
The docs just mention you cannot scale global services:
The scale command enables you to scale one or more replicated services either up or down to the desired number of replicas. This command cannot be applied on services which are global mode.
You can force a rolling update of a service, either globally scheduled or replicated using docker service update --force ${service_name}. Here's an example compose file:
version: '3'
services:
busybox-global:
image: busybox
command: tail -f /dev/null
deploy:
mode: global
busybox-replicated:
image: busybox
command: tail -f /dev/null
deploy:
replicas: 2
Verify it has started:
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
917aefdc910b busybox:latest "tail -f /dev/null" 50 seconds ago Up 31 seconds sched_busybox-global.q44zx0s2lvu1fdduk800e5ini.hzn6jnzh7x539timamphzzw8a
7187fbbde0da busybox:latest "tail -f /dev/null" About a minute ago Up 31 seconds sched_busybox-replicated.1.i4nm7lpr1spmf0aorh1dtcqrc
f04a0062b088 busybox:latest "tail -f /dev/null" About a minute ago Up 31 seconds sched_busybox-replicated.2.oc6zn0ziqg9wyzofokek8eb24
$ docker service ls
ID NAME MODE REPLICAS IMAGE PORTS
gto0d5a6betb sched_busybox-global global 1/1 busybox:latest
yfq5mne0qhtj sched_busybox-replicated replicated 2/2 busybox:latest
$ docker service ps sched_busybox-global
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS
hzn6jnzh7x53 sched_busybox-global.q44zx0s2lvu1fdduk800e5ini busybox:latest bmitch-asusr556l Running Running 49 seconds ago
Force the rolling update:
$ docker service update --force sched_busybox-global
sched_busybox-global
overall progress: 1 out of 1 tasks
q44zx0s2lvu1: running [==================================================>]
verify: Service converged
$ docker service ps sched_busybox-global
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS
zcfocrfjvvux sched_busybox-global.q44zx0s2lvu1fdduk800e5ini busybox:latest bmitch-asusr556l Running Running 7 seconds ago
hzn6jnzh7x53 \_ sched_busybox-global.q44zx0s2lvu1fdduk800e5ini busybox:latest bmitch-asusr556l Shutdown Shutdown 10 seconds ago
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
3c5fe0f79e3d busybox:latest "tail -f /dev/null" About a minute ago Up About a minute sched_busybox-global.q44zx0s2lvu1fdduk800e5ini.zcfocrfjvvuxz6tkge0pn0bq2
917aefdc910b busybox:latest "tail -f /dev/null" 3 minutes ago Exited (137) About a minute ago sched_busybox-global.q44zx0s2lvu1fdduk800e5ini.hzn6jnzh7x539timamphzzw8a
7187fbbde0da busybox:latest "tail -f /dev/null" 3 minutes ago Up 2 minutes sched_busybox-replicated.1.i4nm7lpr1spmf0aorh1dtcqrc
f04a0062b088 busybox:latest "tail -f /dev/null" 3 minutes ago Up 2 minutes sched_busybox-replicated.2.oc6zn0ziqg9wyzofokek8eb24
The same would have worked if I forced an update to the replicated service.