feat(host_metrics source): modify the network collector to expose TCP stats

[aryan9600]

Summary

Modify the network collector in the host_metrics source to expose information about the systems's TCP stack. It now exposes three metrics:

• network_tcp_connections_total: The total number of TCP connections. It includes the state of the connection as a tag.
• network_tcp_tx_queued_bytes_total: The sum of the number of bytes in the send queue across all connections.
• network_tcp_rx_queued_bytes_total: The sum of the number of bytes in the receive queue across all connections.

These metrics are only available for Linux systems as it uses the netlink subsystem.

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

How did you test this PR?

• Unit tests for the code interacting with netlink and for the code writing to the metrics buffer.
• Manual testing by running the change locally with the below config file and comparing the output with ss -a -t on both Linux x86 and arm systems.

sources:
  host_metrics:
    type: host_metrics
    collectors:
      - network
sinks:
  console:
    type: console
    inputs:
      - host_metrics
    encoding:
      codec: text

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the "no-changelog" label to this PR.

Checklist

• Please read our Vector contributor resources.
• If this PR introduces changes Vector dependencies (modifies Cargo.lock), please
  run dd-rust-license-tool write to regenerate the license inventory and commit the changes (if any). More details here.

References

closes #21972

[bits-bot]

All committers have signed the CLA.

[jszwedko]

Thanks @aryan9600 ! Exposing these new metrics seem useful. What do you think of putting them under the existing network collector though? Exporting as network_tcp_*.

[aryan9600]

What do you think of putting them under the existing network collector though?

i wanted to keep it as a separate collector, as these metrics are only available for linux. also, to avoid any changes to the output of users when they upgrade to the newer version with these changes. if its a blocker, then i can move it to the network collector, no issue. let me know :)

[jszwedko]

What do you think of putting them under the existing network collector though?

i wanted to keep it as a separate collector, as these metrics are only available for linux. also, to avoid any changes to the output of users when they upgrade to the newer version with these changes. if its a blocker, then i can move it to the network collector, no issue. let me know :)

I think we already have a precedent of collectors having OS-specific metrics (e.g. filesystem_used_ratio only exists for Linux) so I think they'd be a good fit under collector even if they only exist for Linux.

[pront]

Hi @aryan9600, thank you for this PR!

I noticed big change in Cargo.lock, I wonder if you can roll that file back and apply individual updates for the newly added crates only.

[aryan9600]

a problem with having these TCP metrics inside the network collector is that the latter allows to filter the output metrics using network devices, but the former doesn't support this filtering. this is due to the fact that netlink doesn't return the network interface in the response for SOCK_DIAG messages. we could modify the tests and docs to accommodate for this or create a new collector for these metrics. open to any other suggestions.
cc: @pront @jszwedko

[pront]

Hi @aryan9600, one test is failing. I will take another look at this PR once that is fixed. You can run any test locally with cargo test.