Introduction to Kubernetes

Andy Repton, Mission Critical Engineer @ Schuberg Philis

@SethKarlo

arepton@schubergphilis.com

Agenda

  • Intro
  • Installing dependencies
  • Build our clusters
  • Overview of components (while we wait for the clusters to build)
  • Deploying pods, replicasets, deployments, secrets, statefulsets etc
  • Questions

Intro

What is Kubernetes and why do we care?

Kindly sponsored by 

  • They are allowing us to use their AWS account
  • Anyone found to be abusing the account will be forced to buy everyone else beer!

Everyone gets a cluster!

Everybody gets a user

Commands cheat sheet: http://bit.ly/2s17Mwo

Installing dependencies

Install Kubectl

curl -LO https://storage.googleapis.com/kubernetes-release/release/v1.6.6/bin/darwin/amd64/kubectl

Install kops

brew update && brew install kops

Clone the workshop repo

git clone git@github.com:Seth-Karlo/intro-to-kubernetes-workshop.git
export KOPS_STATE_STORE=s3://devopsdays-ams
export MYNAME=user1
export NAME=${MYNAME}.sbp-demo.com

export AWS_ACCESS_KEY_ID=$YourID
export AWS_SECRET_ACCESS_KEY=$yourkey

Export the Variables we need

 kops create cluster --zones eu-west-1a --node-size t2.medium --master-size t2.medium $NAME && kops update cluster ${NAME} --yes

Build our cluster

And build

(This will take a few minutes)

kubectl get cs

Masters, Nodes and etcd, oh my!

Masters, Nodes and etcd, oh my!

Master components are the brains of the cluster. They compose of:

  • Kube Apiserver: runs a powerful api that all components talk to
  • Kube Controller Manager: orchestrates the controllers of the cluster
  • Kube scheduler: determines where pods should be scheduled

Masters, Nodes and etcd, oh my!

Node components are the brains of the individual nodes. They compose of:

  • Kubelet: Talks to the container runtime to run pods, watches pods for health, gathers statistics for the nodes and the pods.
  • Kube proxy: dynamically rewrites iptables to shuttle traffic in and out of the node

Masters, Nodes and etcd, oh my!

Etcd is a replicated key value store that acts as the state store and clustering manager for kubernetes. Access to this is effectively root access on the cluster, so it should be protected and secured.

Pods

When we think of 'Bottom Up', we start with the node:

Pods

Then we add the container runtime

Pods

And then the containers

Pods

When we move from the 'physical' layer to kubernetes, the logical wrapper around containers is a pod

Pods

  • Pods are the basic building blocks of Kubernetes.
  • A pod is a collection of containers, storage and options dictating how the pod should run.
  • Pods are mortal, and are expected to die in order to rebalance the cluster or to upgrade them.
  • Each pod has a unique IP in the cluster, and can listen on any ports required for your application. 

 

Pods support Health checks and liveness checks. We’ll go through those later

Deploy a pod

$ kubectl create -f pod/pod.yaml

Check it's running:

$ kubectl get pods
NAME      READY     STATUS    RESTARTS   AGE
pod       1/1       Running   0          11s

Run a command inside the pod:

$ kubectl exec -it pod bash
[root@pod /]# ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=51 time=0.925 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=51 time=0.961 ms
^C
--- 8.8.8.8 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 999ms
rtt min/avg/max/mdev = 0.925/0.943/0.961/0.018 ms

Kill your pod:

$ kubectl delete pod pod
pod "pod" deleted

Replica Sets

Replica Sets

  • Replica sets define the number of pods that should be running at any given time.
  • With a replica set, if a pod dies or is killed and the replica set no longer matches the required number, the scheduler will create a new pod and deploy it inside the cluster.
  • If too many pods are running, the replica set will delete a pod to bring it back to the correct number.
  • Replica sets can be adjusted on the fly, to scale up or down the number of pods running.

Deploy a replica set

$ kubectl create -f replicaset.yml
replicaset "replica-set" created

Check your pod

$ k get pods
NAME                READY     STATUS    RESTARTS   AGE
replica-set-l3zbz   1/1       Running   0          1m

Delete your pod

$ k delete pod replica-set-l3zbz
pod "replica-set-l3zbz" deleted

Check your pods again

 $ k get pods
NAME                READY     STATUS    RESTARTS   AGE
replica-set-z0pp4   1/1       Running   0          1m

Let's upgrade our replicaset (I've given you an old version of nginx)

 $ kubectl edit replicaset replica-set


  1 # Please edit the object below. Lines beginning with a '#' will be ignored,
  2 # and an empty file will abort the edit. If an error occurs while saving this file will be
  3 # reopened with the relevant failures.
  4 #
  5 apiVersion: extensions/v1beta1
  6 kind: ReplicaSet
  7 metadata:
  8   creationTimestamp: 2017-06-26T10:02:34Z
  9   generation: 1
 10   labels:
 11     app: replica-set
 12   name: replica-set
 13   namespace: default
 14   resourceVersion: "1724"
 15   selfLink: /apis/extensions/v1beta1/namespaces/default/replicasets/replica-set
 16   uid: 9339e8f5-5a56-11e7-8817-0a75658e3054
 17 spec:
 18   replicas: 1
 19   selector:
 20     matchLabels:
 21       app: replica-set
 22   template:
 23     metadata:
 24       creationTimestamp: null
 25       labels:
 26         app: replica-set
 27     spec:
 28       containers:
 29       - image: nginx:latest
 30         imagePullPolicy: IfNotPresent
 31         name: replica-set
 32         ports:
 33         - containerPort: 80
 34           name: web
 35           protocol: TCP
 36         readinessProbe:
 37           failureThreshold: 3
 38           periodSeconds: 10
 39           successThreshold: 1
 40           tcpSocket:
 41             port: 80
 42           timeoutSeconds: 1
 43         resources: {}
 44         terminationMessagePath: /dev/termination-log
 45         terminationMessagePolicy: File
 46       dnsPolicy: ClusterFirst
 47       restartPolicy: Always
 48       schedulerName: default-scheduler
 49       securityContext: {}
 50       terminationGracePeriodSeconds: 30
 51 status:
 52   availableReplicas: 1
 53   fullyLabeledReplicas: 1
 54   observedGeneration: 1
 55   readyReplicas: 1
 56   replicas: 1

Change 

- image: nginx:1.12
- image: nginx:1.13

to

Let's check our pod:

 $ k get pods
NAME                READY     STATUS    RESTARTS   AGE
replica-set-z0pp4   1/1       Running   0          4m

And the image:

$ kubectl delete pod replica-set-z0pp4
pod "replica-set-z0pp4" deleted
$ kubectl describe pod | grep Image:
    Image:		nginx:1.13

Hmm, that's odd. Let's delete the pod and check the new one

$ kubectl describe pod | grep Image:
    Image:		nginx:1.12

Editing a replica set has no impact on running pods, only new ones

Deployments

  • A Deployment is a copy of a replica set and pods.
  • If a deployment changes, the cluster will automatically create a new replica set with the new version and will automatically live upgrade your pods.
  • A deployment can also be rolled back to a previous version if there is an error.

Deploying a wordpress site

We'll add Volumes and Secrets to our pods

Deploying a wordpress site

$ kubectl create -f persistent-disk.yml
persistentvolumeclaim "mysql-pv-claim" created

We will use persistent volumes for our mysql database

$ kubectl get pvc
NAME             STATUS    VOLUME                                     CAPACITY   ACCESSMODES   STORAGECLASS   AGE
mysql-pv-claim   Bound     pvc-31415c4d-5a59-11e7-8817-0a75658e3054   20Gi       RWO           gp2            55s

Creating secrets

  • A secret is a base64 encoded string or file that is stored in the kubernetes API.
  • You can mount secrets as files inside pods, or make them available as environment variables to the pods.
  • Secrets are not encrypted, and by default are available to every pod in the same namespace, so be careful when putting sensitive information into them.
$ kubectl create secret generic mysql-pass --from-file=password.txt
secret "mysql-pass" created

Creating a secret to hold our mysql password

Deploying mysql

$ kubectl create -f mysql-deployment.yaml
service "wordpress-mysql" created
deployment "wordpress-mysql" created

$ kubectl get pods
NAME                               READY     STATUS    RESTARTS   AGE
wordpress-mysql-1894417608-2k4rm   1/1       Running   0          41s

Now deploy mysql

And check the logs

$ kubectl logs wordpress-mysql-1894417608-2k4rm | tail -1
2017-06-26 10:23:22 0 [Note] mysqld (mysqld 5.6.36) starting as process 1 ...

Deploying wordpress

$ kubectl create -f wordpress-deployment.yaml
service "wordpress" created
persistentvolumeclaim "wp-pv-claim" created
deployment "wordpress" created

Now deploy wordpress

And check the logs

$ kubectl get pods
NAME                               READY     STATUS    RESTARTS   AGE
wordpress-1595585052-9m5vm         1/1       Running   0          55s
wordpress-mysql-1894417608-2k4rm   1/1       Running   0          6m

$ kubectl logs wordpress-1595585052-9m5vm
WordPress not found in /var/www/html - copying now...
WARNING: /var/www/html is not empty - press Ctrl+C now if this is an error!
+ ls -A
lost+found
+ sleep 10
Complete! WordPress has been successfully copied to /var/www/html
AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 100.96.2.8. Set the 'ServerName' directive globally to suppress this message
AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 100.96.2.8. Set the 'ServerName' directive globally to suppress this message
[Mon Jun 26 10:29:00.980026 2017] [mpm_prefork:notice] [pid 1] AH00163: Apache/2.4.10 (Debian) PHP/5.6.30 configured -- resuming normal operations
[Mon Jun 26 10:29:00.980053 2017] [core:notice] [pid 1] AH00094: Command line: 'apache2 -D FOREGROUND'

Services

  • Services expose your pods to other pods inside the cluster or to the outside world.
  • A service uses a combination of labels and selectors to match the pods that it’s responsible for, and then will balance over the pods.
  • Using a service IP, you can dynamically load balance inside a cluster using a service of type ‘ClusterIP’ or expose it to the outside world using a ‘NodePort’ or a ‘LoadBalancer’ if your cloud provider supports it.
  • Creating a service automatically creates a DNS entry, which allows for service discovery inside the cluster.

Exposing our wordpress to the world

$ kubectl get svc wordpress
NAME        CLUSTER-IP       EXTERNAL-IP   PORT(S)   AGE
wordpress   100.70.168.153   <none>        80/TCP    3m

Let's edit that and make it type 'LoadBalancer'

 

$ kubectl edit svc wordpress
service "wordpress" edited
$ kubectl get svc wordpress -o wide
NAME        CLUSTER-IP       EXTERNAL-IP                                                               PORT(S)        AGE       SELECTOR
wordpress   100.70.168.153   a252b84715a5a11e788170a75658e305-2028720367.eu-west-1.elb.amazonaws.com   80:30867/TCP   4m        app=wordpress,tier=frontend

At the moment our service is type 'ClusterIP'

Upgrading our Wordpress

$ kubectl edit deployment wordpress

Change the image from image: wordpress:4.7.3-apache to image: wordpress:4.8.0-apache (the latest)

$ kubectl get pods
NAME                               READY     STATUS        RESTARTS   AGE
wordpress-1321513498-zjmql         0/1       Terminating   0          3m
wordpress-1595585052-93wzw         1/1       Running       0          4s

We can upgrade our pods automatically

Stateful Sets

  • StatefulSets (formerly PetSets) are a way to bring up stateful applications that require specific startup rules in order to function.
  • With a StatefulSet, the pods are automatically added to the Cluster DNS in order to find each other.
  • You can then add startup scripts to determine the order in which the pods will be started, allowing a main db to start first and for workers to join to the main.

Deploying CockroachDB

$ kubectl create -f statefulsets/
service "cockroachdb-public" created
service "cockroachdb" created
poddisruptionbudget "cockroachdb-budget" created
statefulset "cockroachdb" created

Watch your pods start up

 $ kubectl get pods -w
NAME            READY     STATUS     RESTARTS   AGE
cockroachdb-0   0/1       Init:0/1   0          4s

PodDisruptionBudgets

One of the resources created is a 'PodDisruptionBudget'

apiVersion: policy/v1beta1
kind: PodDisruptionBudget
metadata:
  name: cockroachdb-budget
  labels:
    app: cockroachdb
spec:
  selector:
    matchLabels:
      app: cockroachdb
  minAvailable: 67%

If using the 'eviction' type rather than a 'delete' (which statefulsets use), this will prevent you from deleting too many pods.

Testing our CockroachDB cluster

$ kubectl run -it --rm cockroach-client --image=cockroachdb/cockroach --restart=Never --command -- ./cockroach sql --host cockroachdb-public --insecure

root@cockroachdb-public:26257/> SHOW DATABASES;
+--------------------+
|      Database      |
+--------------------+
| crdb_internal      |
| information_schema |
| pg_catalog         |
| system             |
+--------------------+
(4 rows)
root@cockroachdb-public:26257/> CREATE DATABASE IF NOT EXISTS dodams;
root@cockroachdb-public:26257/> CREATE TABLE IF NOT EXISTS dodams.demo (k STRING PRIMARY KEY, v STRING);
CREATE TABLE
root@cockroachdb-public:26257/> UPSERT INTO dodams.demo VALUES('Devops', 'Days'), ('Amsterdam', 'Loves');
INSERT 2
root@cockroachdb-public:26257/> SELECT * FROM dodams.demo;

Test kill a pod

$ kubectl delete pod cockroachdb-2
pod "cockroachdb-2" deleted

Will self heal, in the correct order:

$ kubectl get pods
NAME                               READY     STATUS    RESTARTS   AGE
cockroachdb-0                      1/1       Running   0          29m
cockroachdb-1                      1/1       Running   0          6m
cockroachdb-2                      1/1       Running   0          33s

Other resources

  • DaemonSets
  • ConfigMaps
  • Operators

DaemonSets

  • A daemonset is a special type of deployment that automatically creates one pod on each node in the cluster. If nodes are removed or added to the cluster, the daemonset will resize to match.
  • Daemonsets are useful for monitoring solutions that need to run on each node to gather data for example.

ConfigMaps

  • A config map is a file that is stored inside the kubernetes API.
  • You can mount a config map inside a pod to override a configuration file, and if you update the config map in the API, kubernetes will automatically push out the update file to the pods that are consuming it.
  • Config maps allow you to specify your configuration separately from your code, and with secrets, allow you to move the differences between your DTAP environments into the kubernetes API and out of your docker container

Operators

  • Operators are a new way of running complex stateful applications on Kubernetes by moving the logic of setting up and maintaining an application into a separate pod and utilising the etcd cluster behind kubernetes for state storage and clustering.

Questions and wrap up

Introduction to Kubernetes

By Andy Repton

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Introduction to Kubernetes

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