examples of using go templates to create dynamic service params in stack files

Author: stealthybox

service_templating/1/a

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+# Service Templates
+This stack is currently a valuable example of using Go Templates to modify the ContainerSpec of a swarm service from a stack file. 
+At this point in time, you can template `.Service`, `.Task`, and `.Node` information into `.Hostname`, `.Env`, and `.Mounts`. 
+See the Docker docs on this [here](https://docs.docker.com/engine/reference/commandline/service_create/#create-services-using-templates). 
+
+### volumes:
+There are some caveats with using templating in mount specs with stack files.
+There are issues like [this one](https://github.com/moby/moby/issues/30770#issuecomment-277874145) related to using volumes names.
+Bind mounts work well without modification.
+See `stack.yml` for more context.
+
+### usage:
+```bash
+mkdir 1 2 3
+touch 1/a 2/a 3/a
+docker deploy -c stack.yml mounts
+docker service logs -f mounts_hello
+```
+```
+mounts_hello.3.7hlgvxpla3f6@moby | hi! im hello-3, task-3 of mounts_hello in stack: mounts
+mounts_hello.1.cxkdeu4jhg1n@moby | hi! im hello-1, task-1 of mounts_hello in stack: mounts
+mounts_hello.2.x7yt0o0g5he5@moby | hi! im hello-2, task-2 of mounts_hello in stack: mounts
+mounts_hello.2.x7yt0o0g5he5@moby | total 0
+mounts_hello.3.7hlgvxpla3f6@moby | total 0
+mounts_hello.1.cxkdeu4jhg1n@moby | total 0
+mounts_hello.2.x7yt0o0g5he5@moby | -rwxr-xr-x 1 root root 0 Jun 22 05:29 b
+mounts_hello.1.cxkdeu4jhg1n@moby | -rwxr-xr-x 1 root root 0 Jun 22 05:29 a
+mounts_hello.3.7hlgvxpla3f6@moby | -rwxr-xr-x 1 root root 0 Jun 22 05:29 c
+```
+
+# scripts
+`deploy.sh` removes shrapnel and prints out helpful information. 
+`service.sh` creates a similar service to the stackfile from the command line. 
+You may need to run these scripts 2-3 times depending on how slow your swarm is. (because removal is async)

service_templating/2/b

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+#!/bin/sh
+docker stack rm mounts
+sleep 4
+docker deploy -c stack.yml mounts
+
+sleep 2
+docker service inspect --pretty mounts_hello
+docker service ps --no-trunc mounts_hello
+sleep 2
+docker service logs mounts_hello

service_templating/3/c

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+#!/bin/sh
+docker service rm hello
+docker service create --detach=true \
+ --name hello \
+ --hostname 'hello-{{.Task.Slot}}' \
+ --env SLOT='{{.Task.Slot}}' \
+ --env SERVICE='{{.Service.Name}}' \
+ --replicas 3 \
+ --mount \
+ 'type=bind,src=//local/mounts/{{.Task.Slot}},target=/data' \
+ alpine \
+ sh -c '
+ echo hi! im ${HOSTNAME}, task-${SLOT} of ${SERVICE}
+ ls -l /data
+ sleep 1000
+ '
+
+sleep 2
+docker service inspect --pretty hello
+docker service ps --no-trunc hello
+docker service logs hello

service_templating/README.md

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+# see https://github.com/moby/moby/issues/30770#issuecomment-277874145 for a volumes workaround
+version: '3.2'
+
+services:
+ hello:
+ image: alpine
+ hostname: 'hello-{{.Task.Slot}}'
+ environment:
+ SLOT: '{{.Task.Slot}}'
+ SERVICE: '{{.Service.Name}}'
+ STACK: '{{index .Service.Labels "com.docker.stack.namespace"}}'
+ command:
+ - sh
+ - -c
+ - |
+ echo hi! im $${HOSTNAME}, task-$${SLOT} of $${SERVICE} in stack: $${STACK}
+ ls -l /data
+ sleep 1000
+ volumes:
+ - type: bind
+ source: ./{{.Task.Slot}}
+ target: /data
+ deploy:
+ replicas: 3