Traefik Kubernetes Charmed Operator

This Juju charmed operator written with the Operator Lifecycle Manager Framework, powering ingress controller-like capabilities on Kubernetes.
By ingress controller-like capabilities, we mean that the Traefik Kubernetes charmed operator exposes Juju applications to the outside of a Kubernetes cluster, without relying on the ingress resource of Kubernetes.
Rather, Traefik is instructed to expose Juju applications by means of relations with them.

Setup

These instructions assume you will run the charm on microk8s, and rely on a few plugins, specifically:

sudo snap install microk8s
microk8s enable storage dns
# The following line is required unless you plan to use the `external_hostname` configuration option
microk8s enable metallb 192.168.0.10-192.168.0.100 # You likely want change these IP ranges

Usage

juju deploy ./traefik-k8s_ubuntu-20.04-amd64.charm traefik-ingress --trust --resource traefik-image=ghcr.io/canonical/traefik:2.10.4

Configurations

external_hostname allows you to specify a host for the URL that Traefik will assume is its externally-visible URL, and that will be used to generate the URLs passed to the proxied applications. Note that this has to be a 'bare' hostname, i.e. no http prefix and no :port suffix. Neither are configurable at the moment. (see )
If external_hostname is unspecified, Traefik will use the ingress ip of its Kubernetes service, and the charm will go into WaitingStatus if it does not discover an ingress IP on its Kubernetes service.
The Setup section shows how to optionally set up metallb with MicroK8s, so that Traefik's Kubernetes service will receive an ingress IP.
routing_mode: structured as an enumeration, that allows you to select how Traefik will generate routes:
- path: Traefik will use its externally-visible url and create a route for the requester that will be structure like:
```
http://<external_hostname>:<port>/<requester_model_name>-<requester_application_name>-<requester-unit-index>
```
  For example, an ingress-per-unit provider with http://foo external URL, will provide to the unit my-unit/2 in the my-model model the following URL:
```
http://foo/my-model-my-unit-2
```
- subdomain: Traefik will use its externally-visible url, based on external_hostname or, missing that, the ingress IP, and create a route for the requester that will be structure like:
```
http://<requester_model_name>-<requester_application_name>-<requester-unit-index>.<external_hostname>:<port>/
```
  For example, an ingress-per-unit provider with http://foo:8080 external URL, will provide to the unit my-unit/2 in the my-model model the following URL:
```
http://my-model-my-unit-2.foo:8080
```
  IMPORTANT: With the subdomain routing mode, incoming HTTP requests have the Host header set to match one of the routes.
  Considering the example above, incoming requests are expected to have the following HTTP header:
```
Host: my-model-my-unit-2.foo
```

Relations

Providing ingress proxying

This charmed operator supports two types of proxying:

per-app: This is the "classic" proxying logic of an ingress-controller, load-balancing incoming connections to the various units of the Juju application related via the ingress relation by routing over the latter's Kubernetes service.
per-unit: Traefik will have routes to the single pods of the proxied Juju application related to it via the ingress-per-unit relation.
This type of routing, while somewhat unconventional in Kubernetes, is necessary for applications like Prometheus (where each remote-write endpoint needs to be routed to separately) and beneficial to databases, the clients of which can perform client-side load balancing

Monitoring Traefik itself

The metrics endpoint exposed by Traefik can be scraped by Prometheus over the prometheus_scrape relation interface with:

juju add-relation traefik-ingress:metrics-endpoint prometheus

Contributing

Please see the Juju SDK docs for guidelines on enhancements to this charm following best practice guidelines, and CONTRIBUTING.md for developer guidance.

nobuto-m/traefik-k8s-operator