A small introduction to get started on Kubernetes as a user. This explains the main concepts like pod, deployment and services and gives some hints to help you use kubectl command. These slides were presented in Grenoble Docker meetup in November 2017.

1. Kubernetes for beginners
Dominique Dumont
Debian Project
Nov 2017
Dominique Dumont k8s for beginners

2. Why Kubernetes ?
docker is nice, but containers tend to multiply
needs to manage / orchestrate them
need to handle network setup between all these images (micro
services beget mega network)
handle ”smooth” updates
Solutions: docker swarm, Kubernetes (other ?)
Dominique Dumont k8s for beginners

3. New concepts and terminology
New concepts compared to docker:
pod: a group of containers that provide a functionality
node: a worker machine (or VM). old term: minion
deployment: controls lifecycle of a group of pods (rolling
upgrades)
service: deployment frontend. Configure load-balancer and
external access
Dominique Dumont k8s for beginners

4. Pod in more details
A pod is a group of containers:
share the same IP address.
Must set different listening
ports on each container
declare external ports that
are mapped to container
ports
can mount shared volumes
can be configured with
ConfigMaps and Secrets
through environment
variables or files
Pod
Container
Dominique Dumont k8s for beginners

5. Deployment
A deployment with its
ReplicaSet is a group of
pods (of the same kind):
ReplicaSet ensures
failover
manage liveness and
readiness probes
manage rolling
upgrades
Deployment
Pod
Container
Replica
controler
Pod
Container
Pod
Container
Dominique Dumont k8s for beginners

6. Services
A Service is the external front end of a Deployment:
manage load balancing between the pod instances of a
Deployment
map port between external port (e.g. 80) and container ports
(e.g. 8080)
Deployment
Service
Pod
Container
Replica
controler
Balancer
Load
Pod
Container
Pod
Container
Dominique Dumont k8s for beginners

7. Pod example
Inside a deployment:
spec:
containers:
- name: my-contained-server
image: my-contained-image:latest
imagePullPolicy: Always
livenessProbe:
httpGet: { path: /ping, scheme: HTTPS }
initialDelaySeconds: 15
periodSeconds: 10
timeoutSeconds: 3
readinessProbe: # similar
volumeMounts:
- name: shared-stuff
mountPath: "/var/lib/shared"
- name: side-car
image: side-car:latest
Dominique Dumont k8s for beginners

8. Deployment example
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: super-duper-server
spec:
replicas: 1
strategy:
type: RollingUpdate
rollingUpdate: { maxUnavailable: 0, maxSurge: 2 }
template:
metadata:
name: super-mega-server
labels: # used by Service
my-server: mega-server
spec:
containers:
[ pod specification ]
Dominique Dumont k8s for beginners

9. Service example
apiVersion: v1
kind: Service
metadata:
labels:
name: my-super-service
name: super-service
spec:
ports:
- {port: 443, targetPort: 8090}
type: LoadBalancer
# load balancer target
selector:
my-server: mega-server
Dominique Dumont k8s for beginners

10. Config
namespace: isolated sandboxes within a cluster. Great for
tests
context: associate cluster and namespace
Commands:
$ kubectl config get-contexts
CURRENT NAME CLUSTER AUTHINFO NAMESPACE
minikube minikube minikube
* dev-us-west-2 k-uw2.xxx.com us-west-2-user
dod-dev-us-w2 k-uw2.xxx.com us-west-2-user dod-playground
$ kubectl config use-context dod-dev-us-w2
$ kubectl config set-context ...
Dominique Dumont k8s for beginners

11. Config
namespace: isolated sandboxes within a cluster. Great for
tests
context: associate cluster and namespace
Commands:
$ kubectl config get-contexts
CURRENT NAME CLUSTER AUTHINFO NAMESPACE
minikube minikube minikube
* dev-us-west-2 k-uw2.xxx.com us-west-2-user
dod-dev-us-w2 k-uw2.xxx.com us-west-2-user dod-playground
$ kubectl config use-context dod-dev-us-w2
$ kubectl config set-context ...
Dominique Dumont k8s for beginners

12. Sending config
Create Deployment or services:
$ kubectl apply -f .../file.yaml
Update a deployment:
$ kubectl replace -f .../file.yaml
Dominique Dumont k8s for beginners

13. Kubernetes console
If enabled by admin, cluster can be controled with a web interface
$ kubectl proxy
Starting to serve on 127.0.0.1:8001
Dominique Dumont k8s for beginners

14. Connecting to a container
In enabled by sys admin, you can connect to a container in the
cluster:
$ kubectl exec --namespace francois-sandbox
fco-mode1-n9r-812209105-9wfcs -c omg date
Thu Oct 26 18:01:58 UTC 2017
$ kubectl exec --namespace francois-sandbox
fco-mode1-n9r-812209105-9wfcs -c omg -ti sh / #
Dominique Dumont k8s for beginners

15. Getting logs
Getting log may be the only way to get debug information. To get
log from a container:
$ kubectl logs --namespace francois-sandbox
fco-mode1-n9r-812209105-9wfcs omg --since 10s
$ kubectl logs --namespace francois-sandbox
fco-mode1-n9r-812209105-9wfcs omg -f
Logs from many pods
Problems can occur in any deployed pod. You need to setup a log
aggregator (kibana...)
Dominique Dumont k8s for beginners

16. Auto-completion
Typings all these options and arguments is tedious and error prone.
Add this in your ~/.bashrc
KFILE=/tmp/kube-completion
if [ -f /usr/local/bin/kubectl ]; then
/usr/local/bin/kubectl completion bash > $KFILE
. $KFILE
rm $KFILE
fi
Dominique Dumont k8s for beginners

17. Other tools
You can have your prompt display the current environment:
For a command prompt that shows your context, add this in your
~/.bashrc
NORMAL="[033[00m]"
YELLOW="[e[1;33m]"
__kube_prompt() {
# Get current context
CONTEXT=$(perl -nE ’print if s/current-context: //;’
~/.kube/config)
if [[ -n "$CONTEXT" ]]
then
echo "$YELLOW(k8s: ${CONTEXT})$NORMALn"
fi
}
PS1=$(__kube_prompt)’${USER}@${HOSTNAME}:${PWD/$HOME/~}$ ’
Dominique Dumont k8s for beginners

18. Other tools
You can have your prompt display the current environment:
For a command prompt that shows your context, add this in your
~/.bashrc
NORMAL="[033[00m]"
YELLOW="[e[1;33m]"
__kube_prompt() {
# Get current context
CONTEXT=$(perl -nE ’print if s/current-context: //;’
~/.kube/config)
if [[ -n "$CONTEXT" ]]
then
echo "$YELLOW(k8s: ${CONTEXT})$NORMALn"
fi
}
PS1=$(__kube_prompt)’${USER}@${HOSTNAME}:${PWD/$HOME/~}$ ’
Dominique Dumont k8s for beginners

19. MiniKube
MiniKube lets you play with kubernetes your laptop.
Can use kubernetes console to control your minikube
Note: docker commands deal with a docker daemon running
in minikube, not with your ”regular” docker daemon
Dominique Dumont k8s for beginners