docker run vs. kubectl apply

Márk Sági-Kazár

2022-10-27 @ Let’s Code meetup

Hello!

Márk Sági-Kazár

SRE Tech Lead @ Cisco

@sagikazarmark

https://sagikazarmark.hu

hello@sagikazarmark.hu

Agenda

Containers
Docker
Kubernetes
Summary

Containers

What is a container?

Isolated Linux process (well…usually)
”Virtualized OS”
- Filesystem
- Network
- etc

Container components

Root filesystem (container image)
Command (+argumants)
Environment variables
etc

Advantages of containers

Run applications in isolation
Package applications into portable bundles

OCI: Open Container Initiative

Open standards for containers
Founded by Docker
Linux Foundation project
https://opencontainers.org

OCI specs

Runtime
Image (“Docker image”)
Distribution (“Docker registry”)

https://specs.opencontainers.org

OCI Runtime

Bundle
- Root FS
- Config (command, limits, mounts, etc)
Runtime starts the container ¹

Container runtime: runc

OCI-compatible runtime (ref. implementation)
Extracted from Docker
Single executable
Launches containers as isolated Linux processes

Other OCI runtimes

crun (written in C, can be used as a lib)
runsc (user-space implementation)

Container management

OCI runtime: low-level (manages one container)
Need a „high-level” runtime to
- Manage multiple containers
- Manage container images
- Manage cross-container networking
- etc

Container runtime: containerd

Extracted from Docker
Used runc as the low-level OCI-runtime (in the past)
Pluggable low-level runtimes through shims
Available shims: runc, firecracker, etc

Container runtime: cri-o

Kubernetes-centric container runtime
Integrates OCI-runtimes
Implements CRI: Container Runtime Interface

CRI: Container Runtime Interface

gRPC API for managing containers
Runtimes: containerd, cri-o
Remember dockershim?

Container runtime???

Low-level: OCI-runtime
High-level
- Container „manager” / „engine”
- Interacts with low-level runtimes

Docker

Docker environments

Docker Engine
Docker Swarm
Docker Desktop

Kubernetes

Pods vs containers

Smallest deployable unit
One or more containers
Shared storage and networking
Scaling unit

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
    - name: nginx
      image: nginx:1.14.2
      ports:
        - containerPort: 8