The sidecar injector can be used to inject a sidecar into a Pod via a Mutating Webhook.

The sidecar injector can be installed via Helm. To use the Helm cert-manager is required.

helm repo add ricoberger https://ricoberger.github.io/helm-charts
helm install sidecar-injector ricoberger/sidecar-injector

The configuration for the injected sidecars can be passed to the sidecar injector via the config value in the Helm chart. The following configuration injects the basic auth sidecar:

config: |
  containers:
    - name: basic-auth
      image: ghrc.io/ricoberger/sidecar-injector:basic-auth
      imagePullPolicy: Always
      env:
        - name: BASIC_AUTH_PASSWORD
          valueFrom:
            secretKeyRef:
              key: BASIC_AUTH_PASSWORD
              name: basic-auth-credentials
        - name: BASIC_AUTH_USERNAME
          valueFrom:
            secretKeyRef:
              key: BASIC_AUTH_USERNAME
              name: basic-auth-credentials
      ports:
        - name: http-auth
          containerPort: 4180
      livenessProbe:
        httpGet:
          port: 4180
          path: /health
        initialDelaySeconds: 1
        timeoutSeconds: 5
      readinessProbe:
        httpGet:
          port: 4180
          path: /health
        initialDelaySeconds: 1
        timeoutSeconds: 5
      resources:
        requests:
          cpu: 50m
          memory: 64Mi
        limits:
          cpu: 50m
          memory: 64Mi
  volumes: []
  environmentVariables: []

You can also define a list of volumes and a list of environment variables, which should be set from Pod annotations.

When the sidecar injector is installed in your cluster you have to set some annotation for your Pods:

• sidecar-injector.ricoberger.de: enabled: Enable the sidecar injection for a Pod.
• sidecar-injector.ricoberger.de/containers: <CONTAINER-NAME-1>,<CONTAINER-NAME-2>: Comma-separated list of container names, which should be used from the configuration file.
• sidecar-injector.ricoberger.de/init-containers: <CONTAINER-NAME-1>,<CONTAINER-NAME-2>: Comma-separated list of container names, which should be used from the configuration file as init containers.
• sidecar-injector.ricoberger.de/volumes: <VOLUME-NAME-1>,<VOLUME-NAME-2>: Comma-separated list of volume names, which should be used from the configuration file.

It is possible to set additional environment variables for the injected sidecar via annotations. The environment variables which can be injected must be defined in the environmentVariables section in the config, e.g.

config: |
  environmentVariables:
    - name: ENV_NAME
      container: <CONTAINER-NAME>
      annotation: sidecar-injector.ricoberger.de/envname

With this configuration a user can then use the sidecar-injector.ricoberger.de/envname annotation to set the value of the ENV_NAME environment variable in the specified <CONTAINER-NAME>:

---
kind: Deployment
apiVersion: apps/v1
metadata:
  name: example
  namespace: default
spec:
  selector:
    matchLabels:
      app: example
  template:
    metadata:
      annotations:
        sidecar-injector.ricoberger.de: enabled
        sidecar-injector.ricoberger.de/envname: envvalue

Since the injected sidecars might need different resources depending on the service where they are injected it is also possible to overwrite the CPU Requests / Limits and Memory Requests and Limits via an annotation:

• sidecar-injector.ricoberger.de/containers/<CONTAINER-NAME>/cpurequests
• sidecar-injector.ricoberger.de/containers/<CONTAINER-NAME>/cpulimits
• sidecar-injector.ricoberger.de/containers/<CONTAINER-NAME>/memoryrequests
• sidecar-injector.ricoberger.de/containers/<CONTAINER-NAME>/memorylimits

The same can be done for init containers by using the following annotations:

• sidecar-injector.ricoberger.de/init-containers/<CONTAINER-NAME>/cpurequests
• sidecar-injector.ricoberger.de/init-containers/<CONTAINER-NAME>/cpulimits
• sidecar-injector.ricoberger.de/init-containers/<CONTAINER-NAME>/memoryrequests
• sidecar-injector.ricoberger.de/init-containers/<CONTAINER-NAME>/memorylimits