Michael Schurter 34cb05d297 docs: explain how to use dots in docker labels (#24074) ...

Nomad v1.9.0 (finally!) removes support for HCL1 and the `-hcl1` flag.
See #23912 for details.

One of the uses of HCL1 over HCL2 was that HCL1 allowed quoted keys in
blocks such as env, meta, and Docker's labels:

```hcl
some_block {
  "foo.bar" = "baz"
}
```

This works in HCL1 but is invalid HCL2. In HCL2 you must use a map
instead of a block:

```hcl
some_map = {
  "eggs.spam" = "works!"
}
```

This was such a hassle for users we special cased the `env` and `meta`
blocks to be accepted as blocks or maps in #9936.

However Docker `labels`, being a task config option, is much harder to
special case and commonly needs dots-in-keys for things like DataDog
autodiscovery via Docker container labels:
https://docs.datadoghq.com/containers/docker/integrations/?tab=labels

Luckily `labels` can be specified as a list-of-maps instead:

```hcl
labels = [
  {
    "com.datadoghq.ad.check_names"  = "[\"openmetrics\"]"
    "com.datadoghq.ad.init_configs" = "[{}]"
  }
]
```

So instead of adding more awkward hcl1/2 backward compat code to Nomad,
I just updated the docs to hopefully help people hit by this.

The only other known workaround is dropping HCL in favor of JSON
jobspecs altogether, but that forces a huge migration and maintenance
burden on users:
https://discuss.hashicorp.com/t/docker-based-autodiscovery-with-datadog-how-can-we-make-it-work/18870

2024-09-27 10:02:50 -07:00

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