Welcome to 4th and last blog post on mentoring docker. This week is all about understanding the need for orchestration framework on top of Docker.

Focus points for the week 4

1. What are the challenges with Docker when we have hundreds of applications each with multiple instances running?

0. What happens when application crashes? The expectation is to restart the application automatically. We can do it ourselves by writing a small utility over docker-compose events / docker events. But orchestration frameworks support it by monitoring application health (Kubernetes liveliness-probe).
1. What happens when application crashes and started on another host with another port? Orchestration frameworks provide service discovery frameworks to support this.
2. How to distribute the load when you have multiple copies? Load balancer is used to distribute the load. Ingress is one such example of a load balancer.
3. How to keep x instances of the application running all the time? Orchestration frameworks provide inbuilt support to maintain the instance count by managing replicas (replicaSet in Kubernetes terms).
4. How to run one copy of something per host? There are use cases to run a copy of the application on all available hosts. For e.g. log collector, health monitor, host monitor, etc. Kubernetes provide a way to configure such applications as daemonSet.
5. Where to store app configurations? Kubernetes configMaps provide a way to store non-confidential data as key-value pairs which can be consumed as env variables, command-line arguments, or as configuration files in a volume.
6. How to manage application release process systematically? With Kubernetes we can specify rollout strategy to rollout a feature in a rolling update fashion.
7. How to scale? Kubernetes allows defining autoscaling policies to automatically scale application up/down.
8. How to monitor health of a container? Kubernetes liveliness and readiness probes are used to monitor health of the application.

Exercises for the week 4

There are no exercises for week 4 as orchestration is not covered as part of the program. Feel free to go through following references to understand more about orchestration frameworks.

References