[Proposal] docker service create template support for Node labels

[derteufelqwe]

Currently supported Templates regarding the Nodes
Currently only two templates {{ .Node.ID }} and {{ .Node.Hostname }} are supported. This is nice, but labels would put these templates on another level in terms of possibilities.

How could this look
The template could be something like {{ .Node.Spec.Labels.[label name] }}.
If the label is not found the value "", "null" or "<no value>" (as it's currently done using docker node inspect) should be used.

Summary
Dockers templates for service creation should support node labels.
The result of the template {{ .Node.Spec.Labels.example_label }} should be the same as the output of docker node inspect -f="{{ .Spec.Labels.example_label }}" node_name.

[skechboy]

Great proposal, and highly anticipated :)
Also, as Docker is using Go’s text/template engine, a pipeline can be used for setting a default value if the specific label has null value, for example:

{{ .Node.Spec.Labels.label_name | "default_value" }}

[KevinBLT]

Any news on this?

Absolutely necessary! For now I have a MariaDB docker config, which has a file included that points to a config file mounted from host to get some specific variables for galera cluster. When I could use node labels it would allow me to avoid host bind mounts for config files.

[s4ke]

This feels useful for anyone running stateful apps in swarm. I'd be happy to see if this is something I can contribute to. Any pointers where to look specifically (links to files would be enough) @dperny @thaJeztah ?

[olljanat]

@s4ke I think that it simply folder called for template on root of this Git repo where the code related to this one exists.