[Feature Request] Lists and hash substitutions from settings.yml render

[mkubilus]

Description

When rendering it would be useful to specify more complex substitutions from settings.yml rather than being restricted to only single items.

For instance, I should be able to specify a list of volumes in settings perhaps like so:

myvols: 
  - /tmp:/tmp
  - avol:/amount

and in my docker-compose.yml template refer to this:

services:
  atest:
    image: ${image}
    command: 'echo "test"'
    volumes: ${myvols} 

Steps to reproduce the issue:

1. Specify a list in settings.yml
2. Attempt to refer to the list in docker-compose.yml
3. docker-app render

Describe the results you received: Error: failed to load Compose file: invalid interpolation format for services.atest.volumes: "required variable myvols is missing a value". You may need to escape any $ with another $.

Describe the results you expected: render completes successfully.

Additional information you deem important (e.g. issue happens only occasionally):

Output of docker version:

Client:
 Version:           18.06.1-ce
 API version:       1.38
 Go version:        go1.10.3
 Git commit:        e68fc7a
 Built:             Tue Aug 21 17:24:56 2018
 OS/Arch:           linux/amd64
 Experimental:      false

Server:
 Engine:
  Version:          18.06.1-ce
  API version:      1.38 (minimum version 1.12)
  Go version:       go1.10.3
  Git commit:       e68fc7a
  Built:            Tue Aug 21 17:23:21 2018
  OS/Arch:          linux/amd64
  Experimental:     false

Output of docker-app version:

Version:      v0.6.0
Git commit:   9f9c6680
Built:        Thu Oct  4 13:30:33 2018
OS/Arch:      linux/amd64
Experimental: off
Renderers:    none

Output of docker info:

Containers: 9
 Running: 0
 Paused: 0
 Stopped: 9
Images: 3948
Server Version: 18.06.1-ce
Storage Driver: overlay2
 Backing Filesystem: extfs
 Supports d_type: true
 Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
Swarm: inactive
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 468a545b9edcd5932818eb9de8e72413e616e86e
runc version: 69663f0bd4b60df09991c08812a60108003fa340
init version: fec3683
Security Options:
 apparmor
 seccomp
  Profile: default
Kernel Version: 4.4.0-134-generic
Operating System: Ubuntu 16.04.5 LTS
OSType: linux
Architecture: x86_64
CPUs: 4
Total Memory: 15.55GiB
Name: ******
ID: ZQ3P:BIEJ:D3AJ:5THN:U23Q:3ULB:CFUJ:EFI3:GUS3:HBLS:ZDEB:3C3U
Docker Root Dir: /home/dockerstuff
Debug Mode (client): false
Debug Mode (server): false
Username: ********
Registry: https://index.docker.io/v1/
Labels:
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

WARNING: No swap limit support

[shin-]

Hi @mkubilus

There are some advanced templating features in the experimental build that you may want to try out. For example, you would be able to write the following docker-compose.yml file:

version: '3.5'
services:
  atest:
    image: abc
    command: echo test
    volumes:
{{range $i, $v := .myvols}}
        - {{$v}}
{{end}}

and render using the following command:

DOCKERAPP_RENDERERS=gotemplate docker-app render

Resulting in the following:

version: "3.5"
services:
  atest:
    command:
    - echo
    - test
    image: abc
    volumes:
    - type: bind
      source: /tmp
      target: /tmp
    - type: volume
      source: avol
      target: /amount

[onekiloparsec]

I'd love to see this feature available. Just wondering, for cases where only the values of the list (here myvols) are rendered, why not being able to just write volumes: ${myvols} ?