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* Log collection example for sidecar containers * Add service and update readme * Update 16-sidecar-containers/README.md Co-authored-by: Matthieu Dumont <5095856+Jerska@users.noreply.github.com> |
3 years ago | |
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| 01-sidecar.yml | 3 years ago | |
| README.md | 3 years ago | |
README.md
Sidecar containers: what, why, and how
Introduction
In kubernetes a pod can contain multiple containers:
apiVersion: v1
kind: Pod
metadata:
name: simple-pod
spec:
containers:
- name: container1
image: nginx
- name: container2
image: fluentd
Here we have 2 containers: container1 and container2.
When you have multiple containers in a pod we call them sidecar containers. Most of the time you have a "primary" container, the one with containing your application, and "secondary", hence the sidecar terminology.
All the containers of a given pod share the same network, and can share the same volumes.
Use cases
Sidecars are useful for containers that are tightly coupled. A good use case is when you migrate an app from one machine to containers. The application will have a lot of localhost or 127.0.0.1 hardcoded. So with sidecars you can work around this.
Another use case is to have sidecars helping the main container, like sending logs to a centralized system, sending the metrics to a specific system, doing SSL termination, etc.
Istio, the service mesh tool, installs a sidecar container to do its job: https://istio.io/docs/setup/kubernetes/additional-setup/sidecar-injection/
Exercices
Review and apply the file 01-sidecar.yml.
Connect to the nginx container (kubectl exec -it two-containers -c nginx -- /bin/sh) and look at the file system in /var/log/nginx.
Do the same for the fluentd container and this time look in /logs. What do you see?
Tail the logs from the fluentd pod (kubectl logs -f two-containers -c fluentd) and in another terminal window, send requests to the nginx service with a curl from a separate pod (or nginx's pod itself). What do you see? How do you explain it?
This exercice is taken from the official Kubernetes documentation.
Clean up
kubectl delete service,deployment,pod,configmap --all