Containers

Containers allows developers to test and build applications on any computer by putting it in a container bundled with software code, libraries, and config files

Docker

software used to create and manage containers
can be installed on Linux - daemon can be controlled natively
not supported in RHEL 8

Podman

developed by Red Hat 2018 as an alternative to docker
daemon less, open source, linux native tool to develop, manage and run containers

Red Hat provides a set of CLI tools

podman - directly managing pods and container images (run, stop, start, ps attach, etc)
buildah - for building, pushing, and signing container images
skopeo - copying, inspecting, deleting, signing images
runc - providing container run and build features to podman and buildah
crun - optional runtime that can be configured and give greater flexibility, control & security for rootless containers

images - containers can be created through images and containers can be converted to images
pods - groups of containers deployed together on the host

Basic Commands

dnf install podman -y	install podman
alias docker=podman	used when switching from docker to podman
podman -v	check podman version
podman info	check podman environment (see registries) if loading an image, looks locally, then to registries by order listed

Image --> Run Container --> Remove it

podman search httpd	search container registries for an image
podman pull docker.io/library/httpd	download image from a registry
podman images	list downloaded images
podman run -d --name web1 -p 8080:80 docker.io/library/httpd	create & start a container from an image
podman ps	list running containers
curl localhost:8080 (or web) http://localhost:8080	verify application is accessible
podman stop web1	stop a container gracefully
podman rm -f web1	remove a container

Image --> Create Container --> Start Container

podman pull docker.io/library/httpd	download image from a registry
podman create --name web2 -p 8081:80 docker.io/library/httpd	create a container
podman ps -a	verify status is created -a all containers
podman start web2	start an existing container
podman ps	verify container status is running
curl localhost:8081 (or web) http://localhost:8081	verify application is accessible
podman logs web2	view output generated by container

Quadlet (Modern RHEL10) systemd container management

mkdir -p /etc/containers/systemd	create directory for quadlet definitions
nano /etc/containers/systemd/web3.container … [Unit] Description=Apache Web Container [Container] Image=docker.io/library/httpd ContainerName=web3 PublishPort=8082:80 [Service] Restart=always [Install] WantedBy=multi-user.target	create quadlet container definition file define systemd metadata description define container-specific settings specifies container image assigns name maps host port to container port defines systemd behaviour automatically restart container if it stops definte boot settings allow service to start automatically during boot
systemctl daemon-reload	reload systemd configuration
systemctl enable --now web3.service	enable service at boot and start now
systemctl status web3.service	verify service status
podman ps	verify container status is running
curl localhost:8082 (or web) http://localhost:8082	verify application is accessible