Update tracing to use OTLP/HTTP

[mmkay]

Issue

Prometheus charm grew significantly in size due to a new GRPC dependency introduced by tracing as noticed in #545. Because of that, we reconsidered the protocol used by tracing in canonical/tempo-k8s-operator#53 and decided to use OTLP/HTTP.

Solution

Switch to the new version of charm_tracing and use OTLP/HTTP(S) endpoints of tempo.

Context

This PR implicitly bumps pydantic used by tracing to v2 which is a complete rewrite in Rust. Because rust compiler isn't found in charmcraft pack in this repo I needed to add pydantic to charm-binary-python-packages.

Testing Instructions

First run charmcraft pack to see that prometheus charm is now reduced back to 26MB.

Then, using the packed charm, use the following bundle:

bundle: kubernetes
applications:
  alertmanager:
    charm: alertmanager-k8s
    channel: stable
    revision: 96
    series: focal
    resources:
      alertmanager-image: 84
    scale: 1
    constraints: arch=amd64
    storage:
      data: kubernetes,1,1024M
    trust: true
  catalogue:
    charm: catalogue-k8s
    channel: stable
    revision: 33
    series: focal
    resources:
      catalogue-image: 32
    scale: 1
    options:
      description: "Canonical Observability Stack Lite, or COS Lite, is a light-weight,
        highly-integrated, \nJuju-based observability suite running on Kubernetes.\n"
      tagline: Model-driven Observability Stack deployed with a single command.
      title: Canonical Observability Stack
    constraints: arch=amd64
    trust: true
  grafana:
    charm: grafana-k8s
    channel: stable
    revision: 93
    series: focal
    resources:
      grafana-image: 62
      litestream-image: 43
    scale: 1
    constraints: arch=amd64
    storage:
      database: kubernetes,1,1024M
    trust: true
  loki:
    charm: loki-k8s
    channel: stable
    revision: 105
    series: focal
    resources:
      loki-image: 88
    scale: 1
    constraints: arch=amd64
    storage:
      active-index-directory: kubernetes,1,1024M
      loki-chunks: kubernetes,1,1024M
    trust: true
  prometheus-k8s:
    charm: local:prometheus-k8s-0
    series: focal
    scale: 1
    constraints: arch=amd64
    storage:
      database: kubernetes,1,1024M
    trust: true
  self-signed-certificates:
    charm: self-signed-certificates
    channel: stable
    revision: 57
    scale: 1
    constraints: arch=amd64
  tempo-k8s:
    charm: tempo-k8s
    channel: candidate
    revision: 22
    resources:
      tempo-image: 14
    scale: 1
    constraints: arch=amd64
    storage:
      data: kubernetes,1,1024M
  traefik:
    charm: traefik-k8s
    channel: stable
    revision: 166
    series: focal
    resources:
      traefik-image: 155
    scale: 1
    constraints: arch=amd64
    storage:
      configurations: kubernetes,1,1024M
    trust: true
relations:
- - traefik:ingress-per-unit
  - loki:ingress
- - traefik:traefik-route
  - grafana:ingress
- - traefik:ingress
  - alertmanager:ingress
- - grafana:grafana-source
  - loki:grafana-source
- - grafana:grafana-source
  - alertmanager:grafana-source
- - loki:alertmanager
  - alertmanager:alerting
- - grafana:grafana-dashboard
  - loki:grafana-dashboard
- - grafana:grafana-dashboard
  - alertmanager:grafana-dashboard
- - catalogue:ingress
  - traefik:ingress
- - catalogue:catalogue
  - grafana:catalogue
- - catalogue:catalogue
  - alertmanager:catalogue
- - tempo-k8s:grafana-source
  - grafana:grafana-source
- - prometheus-k8s:certificates
  - self-signed-certificates:certificates
- - tempo-k8s:tracing
  - prometheus-k8s:tracing
- - traefik:metrics-endpoint
  - prometheus-k8s:metrics-endpoint
- - prometheus-k8s:grafana-source
  - grafana:grafana-source

You should be able to see traces in Grafana:

Release Notes

[PietroPasotti]

very nice! have you tested it with and without TLS I presume?

[mmkay]

Correct - tried both scenarios. In both cases I had traces coming in.