Multi-Container Pods

Question 1

What kind of patterns exist for multi-container pods in Kubernetes?

Answer 1

• Ambassador
• Sidecar
• Adapter

Question 2

What are reasons for multi-container pods and what are consequences for the included containers?

Answer 2

• sometimes close-connection between two services needed
• both containers share lifecycle, network and storage of the pod

Question 3

How do we create multi-container pods?

Answer 3

• in yaml add new container in spec section

Question 4

What is a good example of a Sidecar patternß

Answer 4

• deploying a logging agent besides a webserver to collect logs and forward them to a central log server
• additional container with additional functionality

Question 5

What is an example for the Adapter pattern?

Answer 5

• an adapter container that processes logs and standardizes the format
• before sending them forward to the centralized server

Question 6

What is an example for the Ambassador pattern?

Answer 6

• i.e when you use three different databases for different environment (prod, dev, test)
• this connectivity needs to be configured in the application in dependence on the goal environment
• such logic may be outsourced to a separate container within the pod, so that the application can always refer to the database at localhost and your container will proxy the request to the right database

Question 7

With what command can we see the logs of a running application/pod?

Answer 7

kubectl logs app-name -n namespace

Question 8

What happens if any one container in one pod fail?

Answer 8

• the pod restarts
• all containers within a pod are expected to stay alive

Question 9

What is initContainers used for?

Answer 9

• to run a task/process that will run only one time when the pod is first created or a process that waits for an external service or database to be up before the actual application starts

Question 10

How do we configure a initContainer ?

Answer 10

in pod yaml:

spec: 
 containers:
  - name:
initContainers:
 - name: init-myservice
   image: busybox
	 command: ['sh', '-c', 'git clone < some repo that will be used by the application;']

Question 11

How does the initContainer work?

Answer 11

• when pod first created, the initContainer is run
• process in initContainer must run to completion before the real container hosting the application starts

Question 12

Are multiple initContainers possible? What about sequence and failure?

Answer 12

Yes
- each initContainer is then run one at a time in a sequential order
- if any of the initContainer fails to complete, pod is restarted until it succeeds