Can't evaluate fields in template strings

[vivanov1410]

Gentlemen, I started to have issues with format templates after I upgraded docker engine from 1.12 to 1.13.

Steps to reproducte

1. I run a docker service using following command

docker service create --name logspout \
  --network mejai-network \
  --mode global \
  --mount type=bind,src=/var/run/docker.sock,dst=/var/run/docker.sock \
  --env SYSLOG_HOSTNAME='{{index .Config.Labels "com.docker.swarm.service.name"}}' \
  --env SYSLOG_TAG='{{.Name}}' \
  --env SYSLOG_STRUCTURED_DATA='cluster={{index .Config.Labels "ca.surrey.swarm.cluster"}}' \
  gliderlabs/logspout $ELK

Actual result

Error response from daemon: rpc error: code = 3 desc = expanding env failed: expanding env "SYSLOG_HOSTNAME={{index .Config.Labels \"com.docker.swarm.service.name\"}}": template: expansion:1:15: executing "expansion" at <.Config.Labels>: can't evaluate field Config in type *template.Context

But if I run docker inspect --format {{.Config.Labels}} dda42680d044 it all works.

Any ideas?

[michaelshobbs]

Confirmed that this worked in docker 1.12. I fear this is a bit of chicken and egg where the labels aren't available in time. Not sure what we can reasonably do in logspout. Might be worth opening an issue against docker/docker?

docker 1.13 service inspect without env set:

            "Labels": {
                "com.docker.swarm.node.id": "10w0lr46p8q7d5mz2x97qxzkq",
                "com.docker.swarm.service.id": "llu4uvhaqw282edlq1a90c7he",
                "com.docker.swarm.service.name": "logspout",
                "com.docker.swarm.task": "",
                "com.docker.swarm.task.id": "dja3x17ac9e9v8xts27nmcgj8",
                "com.docker.swarm.task.name": "logspout.1.dja3x17ac9e9v8xts27nmcgj8"
            }

[mostolog]

I'm having a similar issue trying to set {{.Service.Name}}-{{.Task.Slot}} as syslog tag on my stack/compose file.

    logging:
      driver: 'syslog'
      options:
        tag: '{{.Service.Name}}-{{.Task.Slot}}'
        syslog-facility: 'local0'

suggestions?

[mostolog]

Seems this have been solved on docker 17.10

[thiagonache]

did you test it? i'm still having issues.

failed to update service prod-swarm_logspout: Error response from daemon: rpc error: code = InvalidArgument desc = expanding env failed: expanding env "SYSLOG_STRUCTURED_DATA=BLABLA@41058 tag=\"bla\" {{ index .Container.Config.Labels \"net.bla.app.tags\" }}\n": template: expansion:1:42: executing "expansion" at <.Container.Config.La...>: can't evaluate field Container in type *template.Context

$ docker -v
Docker version 17.10.0-ce, build f4ffd25

[develar]

docker 17.10 cannot be used in production because contains some critical errors (that fixed in the 17.11, but again, it is edge release and another critical error maybe).

As a solution, I just forked this project and build own image. develar@c9d3571

[zhaoyao91]

Same problem

stack:

version: "3.3"

services:
#  just-log:
#    image: zhaoyao91/just-log
#    environment:
#      INTERVAL: 10000
  logsout:
    image: gliderlabs/logspout
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    command: raw+udp://localhost:55555
    environment:
      LOGSPOUT: ignore
      ALLOW_TTY: "true"
      RAW_FORMAT: "{{.Data}}\n"

error:

failed to update service test-log_logsout: Error response from daemon: rpc error: code = InvalidArgument desc = expanding env failed: expanding env "RAW_FORMAT={{.Data}}\n": template: expansion:1:2: executing "expansion" at <.Data>: can't evaluate field Data in type *template.Context

[sandys]

is there an update for this ? can we use template variables in any environment variables ?

[mkst]

context.go looks to be the file that drives what can be templated. Could this be extended to support additional configuration (e.g. Node.Labels)?

[PowerSurj]

I hit same problem with the expression RAW_FORMAT: {{ index .Config.Labels "com.docker.swarm.service.name" }}
Tested on Docker 19.03.6

After many attempts found that you have to wrap Go Template expressions in another pair of curly braces.
I have no idea why this must be done, neither documentation states you have to do it.
Below expression works and it returns service name
RAW_FORMAT: "{{`{{ index .Container.Config.Labels \"com.docker.swarm.service.name\" }}`}}\n"