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RHCA - EX180

Red Hat Certified Specialist in Containers and Kubernetes

 

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 -m -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 rhscl/mariadb-102-rhel7 \
-v /srv/mariadb:/var/lib/mysql:Z # :Z isn't needed if SELinux manually configured

Basic pod status and names

podman ps

image-1644549207088.png

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

 

image-1644971700185.png

Get more detailed information about the project

oc get all

image-1644971829839.png

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

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

 

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