# FLAMEK8sBakend

A [FLAME](https://github.com/phoenixframework/flame/tree/main) Backend for
Kubernetes. Manages pods as runners in the cluster the app is running in.

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The current implementation is very basic and more like a proof of concept.
More configuration options (resources, etc.) will follow.

## Installation

```elixir
def deps do
  [
    {:flame_k8s_backend, "~> 0.2.1"}
  ]
end
```

## Usage

Configure the flame backend in our configuration.

```elixir
# config.exs
if config_env() == :prod do
  config :flame, :backend, FLAMEK8sBackend
  config :flame, FLAMEK8sBackend, log: :debug
end
```

## Prerequisites

### Env Variables

In order for the runners to be able to join the cluster, you need to configure
a few environment variables on your pod/deployment:

The `POD_NAME` and `POD_NAMESPACE` are used by the backend to get informations
from your pod and use them for the runner pods (e.g. env variables).

```yaml
apiVersion: apps/v1
kind: Deployment
spec:
  selector:
    matchLabels:
      app: myapp
  template:
    spec:
      containers:
        - env:
            - name: POD_NAME
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: metadata.name
            - name: POD_NAMESPACE
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: metadata.namespace
```

### RBAC

Your application needs run as a service account with permissions to manage
pods:

```yaml
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: myapp
  namespace: app-namespace
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: app-namespace
  name: pod-mgr
rules:
  - apiGroups: [""]
    resources: ["pods"]
    verbs: ["create", "get", "list", "delete", "patch"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: myapp-pod-mgr
  namespace: app-namespace
subjects:
  - kind: ServiceAccount
    name: myapp
    namespace: app-namespace
roleRef:
  kind: Role
  name: pod-mgr
  apiGroup: rbac.authorization.k8s.io
---
apiVersion: apps/v1
kind: Deployment
spec:
  template:
    spec:
      serviceAccountName: flame-test
```

### Clustering

Your application needs to be able to form a cluster with your runners. Define
`POD_IP`, `RELEASE_DISTRIBUTION` and `RELEASE_NODE` environment variables on
your pods as follows:

```yaml
apiVersion: apps/v1
kind: Deployment
spec:
  template:
    spec:
      containers:
        - env:
            - name: POD_IP
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: status.podIP
            - name: RELEASE_DISTRIBUTION
              value: name
            - name: RELEASE_NODE
              value: flame_test@$(POD_IP)
```