# Rahti ### Introduction to containers

# Containers
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- All containers on the same host share a single OS kernel, so they use fewer resources than virtual machines
                        - Containers are stateless — modifications inside them are lost
                        - Container images are stored in registries, e.g. <https://hub.docker.com> and <https://quay.io>

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                            <img src="/img/sld-rahti-image37.png" alt="Containers sharing a single host OS kernel.">
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                        # A Pouta VM running a Docker container
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```txt
                        docker run alpine
                        docker run -it alpine
                          whoami
                          du -sh
                          apk add python3
                          ctrl+d
                        ```

- Container runtimes: Docker, Podman, CRI-O

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                        # Multiple containers on one host / cluster
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- Multiple Docker images run on a single machine
                        - …and across a cluster of machines

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                            <img src="/img/sld-rahti-image40.png" alt="Multiple containers running across a cluster of machines.">
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                        # One technology to rule them all
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- Kubernetes orchestrates containers across many machines
                        - OpenShift (OKD) extends Kubernetes
                        - Rahti is CSC's OpenShift OKD platform

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                        # Rahti @ Pouta
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- Rahti is at best as good as the Pouta environment underneath it
                          - SLA
                          - Performance
                        - The architecture gives better scalability and security
                          - The biggest overhead comes from the KVM hypervisor
                          - Bare-metal OpenShift has been under test

📱🔨

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Thank you

Joona Tolonen

servicedesk@csc.fi