RHCA - EX180/EX280

Red Hat Certified Specialist in Containers and Kubernetes

Notes, tips and tricks for the EX180 and EX280 exams.

 

Podman host setup

dnf module install container-tools

dnf install -y buildah

Podman basics

Registry file: /etc/containers/registries.conf

Login to a registry

podman login registry.access.redhat.com

Search for images

podman search mariadb

Inspect images without downloading

skopeo inspect docker://registry.access.redhat.com/rhscl/mariadb-102-rhel7

Download images

podman pull registry.access.redhat.com/rhscl/mariadb-102-rhel7

List images

podman images

Inspect images. *Useful for locating config.user

podman inspect registry.access.redhat.com/rhscl/mariadb-102-rhel7:latest

Configure container volume path

sudo mkdir /srv/mariadb
sudo chown -R 27:27 /srv/mariadb # UID found in podman inspect
sudo semanage fcontext -a -t container_file_t "/srv/mariadb(/.*)"
sudo restorecon -Rv /srv/mariadb

Run image
-d detached
-e per variable
-p local_port:container_port
-v local/path:/path/in/pod

podman run -d -e MYSQL_USER=user \
-e MYSQL_PASSWORD=pass -e MYSQL_DATABASE=db \
-p 33306:3306  \
-v /srv/mariadb:/var/lib/mysql:Z \ # :Z isn't needed if SELinux manually configured
rhscl/mariadb-102-rhel7

Basic pod status and names

podman ps

Enter container in interactive shell

podman exec -it container-name /bin/bash

Commit changes to running image

podman commit container-name image-name

Export image

podman save image-name > /path/to/image.tar

Remove images

podman rmi image-name --force

Restore/Load image

podman load -i /path/to/image.tar

Dockerfile Basics

Container for scanning a network.

# Start with a base image
FROM registry.access.redhat.com/ubi8
# Maintainer information
MAINTAINER ClusterApps <mail@clusterapps.com>
# Run commands to build the container
# Do as much with the fewest RUN lines
RUN yum --assumeyes update && \
yum --assumeyes install \
nmap iproute procps-ng && \
bash && \
yum clean all
# Entrypoint is the command that run when the ccontainer starts
ENTRYPOINT ["/usr/bin/nmap"]
#  The arguments for the entrypoint
CMD ["-sn", "192.168.252.0/24"]

Build the image with a tag

podman build -t notes180 .

List images

podman images

Run the image

podman run localhost/notes180

OpenShift Basics

Setup oc completion

source <(oc completion bash)

Create a new project

oc new-project nginx

Create a new application based on an image

oc new-app bitnami/nginx

Basic information about the project

oc status

 

Get more detailed information about the project

oc get all

Get full details about a pod

oc describe pod/nginx-84654f9574-9gpnt

Get full details about a deployment

oc describe deployment.apps/nginx

Application deployments

Generate a YAML file to use as a base.

oc create deployment nginx --image=bitnami/nginx --dry-run=client -o yaml > newapp.yml

Create a temporary deployment using the YAML file,

oc create -f newapp.yml

Create the service by exposing the deployment

# dry run to add to YAML file
oc expose deployment --port=8080 --dry-run=client nginx -o yaml >> newapp.yml
# run to create the service
oc expose deployment --port=8080 nginx

Expose the service

oc expose svc nginx --dry-run=client -o yaml >> newapp.yml

New app with parameters, as a deployment-config, and with labels (app=database)

oc new-app --name mdb -l app=database -e MYSQL_USER=dbuser -e MYSQL_PASSWORD=SuperAwesomePassword -e MYSQL_DATABASE=dbname bitnami/mysql --as-deployment-config

Delete the temporary application

oc delete all --all

Edit the YAML file and break up the sections into proper YAML.
Add --- at the beginning of a section
Add ... at the end of a section.

The new nginx app YAML file.

---
apiVersion: apps/v1
kind: Deployment
metadata:
  creationTimestamp: null
  labels:
    app: nginx
  name: nginx
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  strategy: {}
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: nginx
    spec:
      containers:
      - image: bitnami/nginx
        name: nginx
        resources: {}
status: {}
...

apiVersion: v1
kind: Service
metadata:
creationTimestamp: null
labels:
app: nginx
name: nginx
spec:
ports:

port: 8080
protocol: TCP
targetPort: 8080
selector:
app: nginx
status:
loadBalancer: {}
...


apiVersion: route.openshift.io/v1
kind: Route
metadata:
creationTimestamp: null
labels:
app: nginx
name: nginx
spec:
port:
targetPort: 8080
to:
kind: ""
name: nginx
weight: null
status: {}
...

Delete API resources defined by a YAML file.

oc delete -f newapp.yml

Using Templates

Get a list of templates

oc get templates -n openshift

Get template details
Review the parameters section for a list of environment variables.

oc describe template -n openshift mariadb-persistent

Create a new application from a template

oc new-app --template=mariadb-persistent \
-p MYSQL_USER=jack -p MYSQL_PASSWORD=password \
-p MYSQL_DATABASE=jack

Check the status of the deployment.

oc get all
oc describe pod/mariadb-1-qlvrj

Source 2 Image

Gety a list of templates and streams

oc new-app -L

Deploy a new app from a git repo

oc new-app php~https://github.com/clusterapps/simpleapp.git

Watch the app get built

oc logs -f buildconfig/simpleapp

Review the deployment with oc get all

NAME                            READY   STATUS      RESTARTS   AGE
pod/mariadb-1-deploy            0/1     Completed   0          16m
pod/mariadb-1-qlvrj             1/1     Running     0          16m
pod/simpleapp-1-build           0/1     Completed   0          2m10s
pod/simpleapp-fb5554fd9-4kgnb   1/1     Running     0          89s
NAME                              DESIRED   CURRENT   READY   AGE
replicationcontroller/mariadb-1   1         1         1       16m
NAME                TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)             AGE
service/mariadb     ClusterIP   10.217.5.246   <none>        3306/TCP            16m
service/simpleapp   ClusterIP   10.217.4.16    <none>        8080/TCP,8443/TCP   2m11s
NAME                        READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/simpleapp   1/1     1            1           2m11s
NAME                                   DESIRED   CURRENT   READY   AGE
replicaset.apps/simpleapp-75c686cbb8   0         0         0       2m11s
replicaset.apps/simpleapp-fb5554fd9    1         1         1       89s
NAME                                         REVISION   DESIRED   CURRENT   TRIGGERED BY
deploymentconfig.apps.openshift.io/mariadb   1          1         1         config,image(mariadb:10.3-el8)
NAME                                       TYPE     FROM   LATEST
buildconfig.build.openshift.io/simpleapp   Source   Git    1
NAME                                   TYPE     FROM          STATUS     STARTED         DURATION
build.build.openshift.io/simpleapp-1   Source   Git@26e2f16   Complete   2 minutes ago   41s
NAME                                       IMAGE REPOSITORY                                                           TAGS     UPDATED
imagestream.image.openshift.io/simpleapp   default-route-openshift-image-registry.apps-crc.testing/nginx2/simpleapp   latest   About a minute ago