ConfigMap

Configuration parameters that are not secret can be put in a ConfigMap.

Input is key value pairs

The ConfigMap key-value pairs can then be read by the app using:

 - Environment variables
 - Container commandline arguments in the Pod configuration
 - using volumes

A config map can contain full configuration files.
 - e.g. a webserver config file

The file can then b mounted using volumes where the application expects
its configuration file.
  - I believe it replaces what was originally loaded.

This is the way to inject configuation setting into containers with changing
the container itself.

Create a properties file.
=========================
use: cat <<EOF>> nameOfFile
This will open a document and add whatever you write until you type EOF

******i.e.
cat <<EOF>> app.properties
driver=jdbc
database-postgres
lookandfeel=1
param.with.hierarchy=xyz
EOF

To add it to K8s

kubectl create configmap app-config -- from-file=app.properties

Using a ConfigMap
=================

cat configmap/reverseproxy.conf

server {
    listen       80;
    server_name  localhost;

    location / {
        proxy_bind 127.0.0.1;
        proxy_pass http://127.0.0.1:3000;
    }

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }
}

kubectl create configmap nginx-config --from-file=configmap/reverseproxy.conf

configmap "nginx-config" created

kubectl get configmap

NAME           DATA      AGE
nginx-config   1         43s



kubectl get configmap nginx-config -o yaml

apiVersion: v1
data:
  reverseproxy.conf: |
    server {
        listen       80;
        server_name  localhost;

        location / {
            proxy_bind 127.0.0.1;
            proxy_pass http://127.0.0.1:3000;
        }

        error_page   500 502 503 504  /50x.html;
        location = /50x.html {
            root   /usr/share/nginx/html;
        }
    }
kind: ConfigMap
metadata:
  creationTimestamp: 2017-12-30T15:24:26Z
  name: nginx-config
  namespace: default
  resourceVersion: "229515"
  selfLink: /api/v1/namespaces/default/configmaps/nginx-config
  uid: 85997ecd-ed75-11e7-9ced-080027875e97

cat configmap/nginx.yml

apiVersion: v1
kind: Pod
metadata:
  name: helloworld-nginx
  labels:
    app: helloworld-nginx
spec:
  containers:
  - name: nginx
    image: nginx:1.11
    ports:
    - containerPort: 80
    volumeMounts:
    - name: config-volume
      mountPath: /etc/nginx/conf.d
  - name: k8s-demo
    image: wardviaene/k8s-demo
    ports:
    - containerPort: 3000
  volumes:
    - name: config-volume
      configMap:
        name: nginx-config
        items:
        - key: reverseproxy.conf
          path: reverseproxy.conf


kubectl create -f configmap/nginx.yml

pod "helloworld-nginx" created


kubectl create -f configmap/nginx-service.yml

service "helloworld-nginx-service" created

minikube service helloworld-nginx-service --url

http://192.168.99.100:31342

kubectl get pod

NAME               READY     STATUS    RESTARTS   AGE
database           1/1       Running   0          13h
helloworld-nginx   2/2       Running   0          2m

curl http://192.168.99.100:31342
Hello World!

curl http://192.168.99.100:31342 -vvvv

* Rebuilt URL to: http://192.168.99.100:31342/
*   Trying 192.168.99.100...
* Connected to 192.168.99.100 (192.168.99.100) port 31342 (#0)
> GET / HTTP/1.1
> Host: 192.168.99.100:31342
> User-Agent: curl/7.43.0
> Accept: */*
>
< HTTP/1.1 200 OK
< Server: nginx/1.11.13
< Date: Sat, 30 Dec 2017 15:33:11 GMT
< Content-Type: text/html; charset=utf-8
< Content-Length: 12
< Connection: keep-alive
< X-Powered-By: Express
< ETag: W/"c-7Qdih1MuhjZehB6Sv8UNjA"
<
* Connection #0 to host 192.168.99.100 left intact
Hello World!


kubectl exec -i -t helloworld-nginx -c nginx --
root@helloworld-nginx:/#

Get the processes running in a pod.
===================================

kubectl exec -i -t helloworld-nginx -c nginx -- bash
root@helloworld-nginx:/# ps x
  PID TTY      STAT   TIME COMMAND
    1 ?        Ss     0:00 nginx: master process nginx -g daemon off;
    6 pts/0    Ss     0:00 bash
   10 pts/0    R+     0:00 ps x

PID 1 is the process created by the configMap.

This reverseproxy.conf file is now inside the container at etc.nginx/conf.d/:

cat /etc/nginx/conf.d/reverseproxy.conf

server {
    listen       80;
    server_name  localhost;

    location / {
        proxy_bind 127.0.0.1;
        proxy_pass http://127.0.0.1:3000;
    }

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }
}







....