Docker + Kubernetes

For some time, I wanted to take a look at kubernetes. There is a lot of talking about microservices in the cloud and after attending some meetups, I wasnt sure what was all this about so I signed for kodekloud to learn about it.

So far, I have completed the beginners course for Docker and Kubernetes. To be honest, I think the product is very good value for money.

I have been using docker a bit the last couple of months but still wanted to take a bit more info to improve my knowledge.

I was surprised when reading that kubernets pods rely on docker images.

Docker Notes

Docker commands

docker run -it xxx (interactive+pseudoterminal)
docker run -d xxx (detach)
docker attach ID (attach)
docker run --name TEST xxx (provide name to container)
docker run -p 80:5000 xxx (maps host port 80 to container port 5000)

docker run -v /opt/datadir:/var/lib/mysql mysql (map a host folder to container folder for data persistence)

docker run -e APP_COLOR=blue xxx (pass env var to the container)
docker inspect "container"  -> check IP, env vars, etc
docker logs "container"

docker build . -t account_name/app_name
docker login
docker push account_name/app_name

docker -H=remote-docker-engine:2375 xxx

cgroups: restrict resources in container
  docker run --cpus=.5  xxx (no more than 50% CPU)
  docker run --memory=100m xxx (no more than 100M memory)

Docker File

----
FROM Ubuntu
ENTRYPOINT ["sleep"]
CMD ["5"]        --> if you dont pass any value in "docker run .." it uses by default 5.
----

Docker Compose

$ cat docker-compose.yml
version: "3"
services:
 db:
  image: postgres
  environment:
    - POSTGRES_PASSWORD=mysecretpassword
 wordpress:
  image: wordpress
  links:
    - db
  ports:
    - 8085:80


verify file: $ docker-compose config

Docker Volumes

docker volume create NAME  --> create /var/lib/docker/volumes/NAME

docker run -v NAME:/var/lib/mysql mysql  (docker volume)
or
docker run -v PATH:/var/lib/mysql mysql  (local folder)
or
docker run --mount type=bind,source=/data/mysql,target=/var/lib/mysql mysql

Docker Networking

networks: --network=xxx
 bridge (default)
 none   isolation
 host (only communication with other containers)   

docker network create --driver bridge --subnet x.x.x.x/x NAME
docker network ls
               inspect

Docker Swarm

I didnt use this, just had the theory. This is for clustering docker hosts: manager, workers.

   manager: docker swarm init
   workers: docker swarm join --token xxx
   manager: docker service create --replicas=3 my-web-server

Kubernetes Notes

container + orchestration
 (docker)    (kubernetes)

node: virtual or physical, kube is installed here
cluster: set of nodes
master: node that manage clusters

kube components:
  api,
  etcd (key-value store),
  scheduler (distribute load),
  kubelet (agent),
  controller (brain: check status),
  container runtime (sw to run containers: docker)

master: api, etcd, controller, scheduler,
   $ kubectl cluster-info
           get nodes -o wide (extra info)
node: kubelet, container

Setup Kubernetes with minikube

Setting up kubernetes doesnt look like an easy task so there are tools to do that like microk8s, kubeadm (my laptop needs more RAM, can’t handle 1master+2nodes) and minikube.

minikube needs: virtualbox(couldnt make it work with kvm2…) and kubectl

Install kubectl

I assume virtualbox is already installed

$ curl -LO "https://storage.googleapis.com/kubernetes-release/release/$(curl -s https://storage.googleapis.com/kubernetes-release/release/stable.txt)/bin/linux/amd64/kubectl"

$ chmod +x ./kubectl
$ sudo mv ./kubectl /usr/local/bin/kubectl
$ kubectl version --client

Install minikube

$ grep -E --color 'vmx|svm' /proc/cpuinfo   // verify your CPU support 
                                               virtualization
$ curl -Lo minikube https://storage.googleapis.com/minikube/releases/latest/minikube-linux-amd64 \
>   && chmod +x minikube
$ sudo install minikube /usr/local/bin/

Start/Status minikube

$ minikube start --driver=virtualbox  --> it takes time!!!! 2cpu + 2GB ram !!!!
😄  minikube v1.12.3 on Debian bullseye/sid
✨  Using the virtualbox driver based on user configuration
💿  Downloading VM boot image ...
    > minikube-v1.12.2.iso.sha256: 65 B / 65 B [-------------] 100.00% ? p/s 0s
    > minikube-v1.12.2.iso: 173.73 MiB / 173.73 MiB [] 100.00% 6.97 MiB p/s 25s
👍  Starting control plane node minikube in cluster minikube
💾  Downloading Kubernetes v1.18.3 preload ...
    > preloaded-images-k8s-v5-v1.18.3-docker-overlay2-amd64.tar.lz4: 510.91 MiB
🔥  Creating virtualbox VM (CPUs=2, Memory=2200MB, Disk=20000MB) ...
🐳  Preparing Kubernetes v1.18.3 on Docker 19.03.12 ...
🔎  Verifying Kubernetes components...
🌟  Enabled addons: default-storageclass, storage-provisioner
🏄  Done! kubectl is now configured to use "minikube"

$ minikube status
minikube
type: Control Plane
host: Running
kubelet: Running
apiserver: Running
kubeconfig: Configured

$ kubectl get nodes
NAME       STATUS   ROLES    AGE     VERSION
minikube   Ready    master   5m52s   v1.18.3

$ minikube stop  // stop the virtualbox VM to free up resources once you finish

Basic Test

$ kubectl create deployment hello-minikube --image=k8s.gcr.io/echoserver:1.10
deployment.apps/hello-minikube created

$ kubectl get deployments
NAME             READY   UP-TO-DATE   AVAILABLE   AGE
hello-minikube   1/1     1            1           22s

$ kubectl expose deployment hello-minikube --type=NodePort --port=8080
service/hello-minikube exposed

$ minikube service hello-minikube --url
http://192.168.99.100:30020

$ kubectl delete services hello-minikube
$ kubectl delete deployment hello-minikube
$ kubectl get pods

Pods

Based on documentation:

Pods are the smallest deployable units of computing that you can create and manage in Kubernetes.
A Pod is a group of one or more containers, with shared storage/network resources, and a specification for how to run the containers. A Pod's contents are always co-located and co-scheduled, and run in a shared context. A Pod models an application-specific "logical host": it contains one or more application containers which are relatively tightly coupled. In non-cloud contexts, applications executed on the same physical or virtual machine are analogous to cloud applications executed on the same logical host.

$ kubectl run nginx --image=nginx
$ kubectl describe pod nginx
$ kubectl get pods -o wi
$ kubectl delete pod nginx

Pods – Yaml

Pod yaml structure:

pod-definition.yml:
---
apiVersion: v1
kind: (type of object: Pod, Service, ReplicatSet, Deployment)
metadata: (only valid k-v)
 name: myapp-pod
 labels: (any kind of k-v)
   app: myapp
   type: front-end
spec:
  containers:
   - name: nginx-container
     image: nginx

Example:

$ cat pod.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: nginx
  labels:
    app: nginx
    type: frontend
spec:
  containers:
  - name: nginx
    image: nginx

$ kubectl apply -f pod.yaml 
$ kubectl get pods

Replica-Set

Based on documentation:

A ReplicaSet's purpose is to maintain a stable set of replica Pods running at any given time. As such, it is often used to guarantee the availability of a specified number of identical Pods.

> cat replicaset-definition.yml
---
 apiVersion: apps/v1
 kind: ReplicaSet
 metadata:
   name: myapp-replicaset
   labels:
     app: myapp
     type: front-end
 spec:
   template:
     metadata:      -------
       name: nginx         |
       labels:             |
         app: nginx        |
         type: frontend    |-> POD definition
     spec:                 |
       containers:         |
       - name: nginx       |
         image: nginx  -----
   replicas: 3
   selector:       <-- main difference from replication-controller
     matchLabels:
       type: front-end
       
> kubectl create -f replicaset-definition.yml
> kubectl get replicaset
> kubectl get pods

> kubectl delete replicaset myapp-replicaset

How to scale via replica-set

> kubectl replace -f replicaset-definition.yml  (first update file to replicas: 6)

> kubectl scale --replicas=6 -f replicaset-definition.yml  // no need to modify file

> kubectl scale --replicas=6 replicaset myapp-replicaset   // no need to modify file

> kubectl edit replicaset myapp-replicaset (NAME of the replicaset!!!)

> kubectl describe replicaset myapp-replicaset

> kubectl get rs new-replica-set -o yaml > new-replica-set.yaml ==> returns the rs definition in yaml!

Deployments

Based on documentation:

A Deployment provides declarative updates for Pods ReplicaSets.
You describe a desired state in a Deployment, and the Deployment Controller changes the actual state to the desired state at a controlled rate. You can define Deployments to create new ReplicaSets, or to remove existing Deployments and adopt all their resources with new Deployments.

Example:

cat deployment-definition.yml
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-deployment
  labels:
    app: myapp
    type: front-end
spec:
  template:
    metadata:
      name: myapp-pod
      labels:
        app: myapp
        type: front-end
    spec:
      containers:
      - name: nginx-controller
        image: nginx
  replicas: 3
  selector:
    matchLabels:
      type: front-end


> kubectl create -f deployment-definition.yml
> kubectl get deployments
> kubectl get replicaset
> kubectl get pods

> kubectl get all

Update/Rollback

From documentation.

By default, it follows a “rolling update”: destroy one, create new one. So this doesnt cause an outage

$ kubectl create -f deployment.yml --record
$ kubectl rollout status deployment/myapp-deployment
$ kubectl rollout history deployment/myapp-deployment
$ kubectl rollout undo deployment/myapp-deployment ==> rollback!!!

Networking

Not handled natively by kubernetes, you need another tool like calico, weave, etc. More info here. This has not been covered in details yet. It looks complex (a network engineer talking…)

Services

Based on documentation:

An abstract way to expose an application running on a set of Pods as a network service.
With Kubernetes you don't need to modify your application to use an unfamiliar service discovery mechanism. Kubernetes gives Pods their own IP addresses and a single DNS name for a set of Pods, and can load-balance across them.

types:
   NodePort: like docker port-mapping
   ClusterIP:
   LoadBalancer

Examples:

nodeport
--------
service: like a virtual server
  targetport - in the pod: 80
  service - 80
  nodeport: 30080 (in the node)
  
service-definition.yml
apiVersion: v1
kind: Service
metadata:
  name: mypapp-service
spec:
  type: NodePort
  ports:
  - targetPort: 80
    port: 80
    nodePort: 30080  (range: 30000-32767)
  selector:
    app: myapp
    type: front-end

> kubectl create -f service-definition.yml
> kubectl get services
> minikube service mypapp-service


clusterip: 
---------
service-definition.yml
apiVersion: v1
kind: Service
metadata:
  name: back-end
spec:
  type: ClusterIP
  ports:
  - targetPort: 80
    port: 80
  selector:
    app: myapp
    type: back-end


loadbalance: gcp, aws, azure only !!!!
-----------
service-definition.yml
apiVersion: v1
kind: Service
metadata:
  name: back-end
spec:
  type: LoadBalancer
  ports:
  - targetPort: 80
    port: 80
    nodePort: 30080
  selector:
    app: myapp


> kubectl create -f service-definition.yml
> kubectl get services

Microservices architecture example

Diagram
=======

voting-app     result-app
 (python)       (nodejs)
   |(1)           ^ (4)
   v              |
in-memoryDB       db
 (redis)       (postgresql)
    ^ (2)         ^ (3)
    |             |
    ------- -------
          | |
         worker
          (.net)

1- deploy containers -> deploy PODs (deployment)
2- enable connectivity -> create service clusterIP for redis
                          create service clusterIP for postgres
3- external access -> create service NodePort for voting
                      create service NodePort for result

Code here. Steps:

$ kubectl create -f voting-app-deployment.yml
$ kubectl create -f voting-app-service.yml

$ kubectl create -f redis-deployment.yml
$ kubectl create -f redis-service.yml

$ kubectl create -f postgres-deployment.yml
$ kubectl create -f postgres-service.yml

$ kubectl create -f worker-deployment.yml

$ kubectl create -f result-app-deployment.yml
$ kubectl create -f result-app-service.yml

Verify:

$ minikube service voting-service --url
http://192.168.99.100:30004
$ minikube service result-service --url
http://192.168.99.100:30005