Collector fails to expand env vars when the value is an IPv6 address with trailing double colon

[congiv]

Describe the bug

On startup, the collector fails to expand env vars when the value is an IPv6 address with trailing double colon. It treats the value as a map instead of a string.

Steps to reproduce

In my environment, I see this when the collector Pod's IPv6 address has a trailing double colon. Given MY_POD_IP=1111:1111:1111:1111:1111::, this fails to expand:

config:
  receivers:
    zipkin:
      endpoint: '[${env:MY_POD_IP}]:9411'

If you don't have an environment where you can get a IPv6 Pod, you can also reproduce like so:

extraEnvs:
- name: MY_MOCK_IP
  value: '1111:1111:1111:1111:1111::'
# ...
config:
  receivers:
    zipkin:
      endpoint: '[${env:MY_MOCK_IP}]:9411'

What did you expect to see?

The collector start successfully with its config expanded, regardless of whether the Pod's IPv6 address has a leading or trailing double colon.

What did you see instead?

Error: failed to resolve config: cannot resolve the configuration: expanding ${env:MY_POD_IP}: expected convertable to string value type, got map["1111:1111:1111:1111:1111:":<nil>](map[string]interface {})
2024/07/12 17:54:20 collector server run finished with error: Error: failed to resolve config: cannot resolve the configuration: expanding ${env:MY_POD_IP}: expected convertable to string value type, got map["1111:1111:1111:1111:1111:":<nil>](map[string]interface {})

What version did you use?

0.104.0

What config did you use?

config:
  receivers:
    zipkin:
      endpoint: '[${env:MY_POD_IP}]:9411'

Environment

Kubernetes Version: 1.28.11-eks-db838b0
Helm Chart Version: 0.97.1
Docker Image Version: otel/opentelemetry-collector-contrib:0.104.0

Additional context

Looks like this may have been partially resolved with #10343

[evan-bradley]

Thanks for the detailed report @congiv. This is happening due to the fact that :: is the confmap delimiter for config paths (e.g. dist::version indicates the version key under the dist map). I'll let others chime in here if they know a better solution, but if you have the ability to manipulate the environment variable in any way before it reaches the Collector, you can try to wrap it in a string.

I was able to reproduce your issue locally and setting something like MY_POD_IP="'1111:1111:1111:1111:1111::'", where the value is seen as quoted by the YAML parser, allowed the Collector to recognize the IP as a string.

[evan-bradley]

This may also be solved by #10603.