Kubernetes Questions – Please answer them

What is the Difference between a Persistent Volume and a Storage Class?

What happens when pods are killed, is the data persisted - How do you test this?

What is the difference between a Service and an Ingress?

By default, Docker uses host-private networking, so containers can talk to other containers only if they are on the same machine.

If you check the pod ip and there is an open containerPort then you should be able to access it via the node - with curl.

What happens when a node dies? The pods die with it, and the Deployment will create new ones, with different IPs. This is the problem a Service solves.

A Kubernetes Service is an abstraction which defines a logical set of Pods running somewhere in your cluster, that all provide the same functionality

When created, each Service is assigned a unique IP address (also called clusterIP)

This address is tied to the lifespan of the Service, and will not change while the Service is alive

communication to the Service will be automatically load-balanced

  • targetPort: is the port the container accepts traffic on
  • port: is the abstracted Service port, which can be any port other pods use to access the Service

Note that the Service IP is completely virtual, it never hits the wire

Kubernetes supports 2 primary modes of finding a Service - environment variables and DNS - DNS requires a COreDNS addon

Ingress is...

An API object that manages external access to the services in a cluster, typically HTTP

How do you know the size of the PV's to create for the PVC's of a helm chart?

Are helm chart declarative or imperitive?

What is a kubernetes operator?

How do you start a new mysql docker container with an existing data directory?

Usage against an existing databaseIf you start your mysql container instance with a data directory that already contains a database (specifically, a mysql subdirectory), the $MYSQL_ROOT_PASSWORD variable should be omitted from the run command line; it will in any case be ignored, and the pre-existing database will not be changed in any way.

The above did not work for me.

trademate-db_1   | Initializing database
trademate-db_1   | 2020-01-16T05:59:38.689547Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
trademate-db_1   | 2020-01-16T05:59:38.690778Z 0 [ERROR] --initialize specified but the data directory has files in it. Aborting.
trademate-db_1   | 2020-01-16T05:59:38.690818Z 0 [ERROR] Aborting
trademate-db_1   | 
trademate_trademate-db_1 exited with code 1

How do you view the contents of a docker volume?

https://docs.docker.com/engine/reference/commandline/volume_inspect/

You can't do this without a container for named volumes (the one's docker manages). So kak...https://stackoverflow.com/questions/34803466/how-to-list-the-content-of-a-named-volume-in-docker-1-9

How do you run python debugger and attach inside a docker container?

Its a mess up...just develop locally

If you were mounting a conf file into an nginx image from docker-compose - how do you do that in production? Do you bake it into the image?

Yes you should.

Do something like this:

FROM nginx:1.17

COPY ./config/nginx/conf.d /etc/nginx/conf.d

# Remove default config
RUN rm /etc/nginx/conf.d/default.conf 

How do you deploy all the k8s spec files in a folder at once? If not is there a specific order to deploy them in?

This Service should exists before the replicas - as it adds environment variables to containers on the pods in the replicaset based on services created.

Should gunicorn and nginx containers be in the same pod?