feat: add agent metadata

[ammario]

Resolves #3480

resource "coder_agent" "main" {
  ...
  metadata {
    display_name = "Process Count"
    key  = "process_count"
    script = "ps aux | wc -l"
    interval = 1
    timeout = 1
  }

  metadata {
    display_name = "Load Average"
    key  = "load"
    script = "awk '{print $1}' /proc/loadavg"
    interval = 1
    timeout = 1
  }

  metadata {
    display_name = "Disk Usage"
    key  = "disk"
    script = "df -h | awk '$6 ~ /^\\/$/ { print $5 }'"
    interval = 1
    timeout = 1
  }
}

Now

• Publish new version of our terraform provider
• Create endpoint for streaming metadata updates
• Write basic, acceptable frontend
• Show errors correctly in the frontend
• Write stories for the frontend!
• Get CollectedAt on the server and send age in seconds to avoid issues caused by time drift between the agent, server, and browser. Also this protects the integrity of the system if coder is ran close to a black hole.
• Write docs
• Mark as alpha

Later

• Update example templates to showcase dynamic metadata
• Allow showing "expanded view" of metadata of everything passed the newline

[matifali]

What do you mean by dynamic metadata?
For example, indexing the 'options' map can show the currently selected coder_parameter.
Is it something like changing inside the workspace like any ENV_VARIABLE?

[ammario]

@matifali — see screenshot I added to original post.

[kylecarbs]

If someone has a lot of metadata, I could see us wanting to debounce some of the requests... e.g. 5 things polling each second * 1000 workspaces = a lot of requests

[ammario]

I considered this but didn't want to pursue optimizing it immediately because the feature is very optional and there's a clear path to adding a WebSocket endpoint to improve performance when the time comes.

[ammario]

A WebSocket endpoint would add substantial complexity (making this harder to review...) and bug risk.

[kylecarbs]

How is this possible?

[ammario]

See new comment

[ammario]

@kylecarbs — made some minor changes, and fixed one concurrency bug... you should take another look at the short diff.

[kylecarbs]

Why use DoChan instead of Do?

[ammario]

It's to not block the loop, and a bit cleaner than wrapping the whole thing in a goroutine.