kube-sidecar-injector

kube-sidecar-injector

Initial implementation of the sidecar injector for k8s.

TL;DR

1. With configuration like this kube-sidecar-injector will make sure that any container that runs in EKS fargate will have prometheus node-exporter sidecar running next to it:

   inject:
     - name: inject-node-exporter
   
       labelSelector:
         matchExpressions:
           - key: eks.amazonaws.com/fargate-profile
             operator: Exists
   
       namespaceSelector:
         matchExpressions:
           - key: kubernetes.io/metadata.name
             operator: NotIn
             values: [kube-system]
   
       labels:
         flashbots.net/prometheus-node-exporter: true
   
       containers:
         - name: node-exporter
           image: prom/node-exporter:v1.7.0
           args: [
             "--log.format", "json",
             "--web.listen-address", ":9100",
           ]
           ports:
             - name: node-exporter
               containerPort: 9100
           resources:
             requests:
               cpu: 10m
               memory: 64Mi
   

2. In conjunction with trust-manager this will allow to automatically mount root CA in every pod:

   inject:
     - name: inject-internal-ca
   
       volumes:
         - name: internal-ca
           configMap:
             name: internal-ca
   
       volumeMounts:
         - mountPath: /usr/local/share/ca-certificates
           name: internal-ca
           readOnly: true
   
         - mountPath: /etc/ssl/certs/internal-ca.crt
           name: internal-ca
           subPath: internal-ca.crt
           readOnly: true
   

Caveats

• Single webhook configuration can be configured to apply multiple injection rules. However, if these rules should interact somehow (for example rule A introduces changes that rule B is supposed to act upon) then these rules should be placed into separate webhooks.

  See k8s webhook reinvocation policy for the details.

• It's not possible for the webhook to know at the runtime whether the patch it generates is invalid.

  For example, if you try to inject a container that has port name of more than 15 characters long k8s will not allow the modified pod to be deployed.

  In situations like this, k8s will infinitely attempt the webhook admission, without ever creating the pod. In order to troubleshoot this issue it could help to see actual underlying error from k8s with:

  kubectl get events