DO180 "Introduction to Containers, Kubernetes, and Red Hat OpenShift" notes in the margin

tags: `red hat, openshift, docker, containers`

Course description: DO180 Introduction to Containers, Kubernetes, and Red Hat OpenShift

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Table of contents

DO180 "Introduction to Containers, Kubernetes, and Red Hat OpenShift" notes in the margin
- Table of contents

HTTPD catches SIGWINCH window change signal and gracefully stop
Graceful Stop httpd with WINCH signal

Container Namespaces – Deep Dive into Container Networking

Image Not Showing Possible Reasons

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habr blog: сеть контейеров это просто

4. Managing Container Images

Red Hat Container Registry Authentication

docker login https://registry.redhat.io
Username: myrhusername
Password:  xxxxxxxxxxx

/etc/containers/registries.conf

How to get a list of images on docker registry v2

jq is a lightweight and flexible command-line JSON processor.

jq Download page

mkdir ~/bin
wget https://github.com/stedolan/jq/releases/download/jq-1.6/jq-linux64 -O ~/bin/jq
chmod +x ~/bin/jq

http://<ip/hostname>:<port>/v2/_catalog

curl -X GET https://myregistry:5000/v2/_catalog
> {"repositories":["redis","ubuntu"]}
curl -X GET https://myregistry:5000/v2/ubuntu/tags/list
> {"name":"ubuntu","tags":["14.04"]}

Docker Registry HTTP API V2

Docker Registry HTTP API V2 docs

https://www.docker.com/blog/checking-your-current-docker-pull-rate-limits-and-status/

bash script to demonstrate auth in registry

Listing image tags for Red Hat's Container Registry

Docker Registry CLI - Provides search functionality for Docker Registry (UI and CLI)

Official rhscl/httpd-24-rhel7 docker image

USING RED HAT SOFTWARE COLLECTIONS 3 CONTAINER IMAGES
USING RED HAT SOFTWARE COLLECTIONS 2.4 CONTAINER IMAGES

Docker Registry This is DEPRECATED! Please go to https://github.com/docker/distribution

Docker Distribution: The Docker toolset to pack, ship, store, and deliver content

propose registry search functionality #206

Docker Registry User Interface

Using in-home Registry without authentication is a Security Problem
Anatomy of a hack: Docker Registry

[RFP] replace catalog API functionality

https://access.redhat.com/RegistryAuthentication
https://access.redhat.com/terms-based-registry/#

5. Creating Custom Container Images

https://docs.docker.com/storage/storagedriver/overlayfs-driver/
https://developers.redhat.com/products/rhel/ubi/
https://www.redhat.com/en/blog/introducing-red-hat-universal-base-image
https://habr.com/ru/company/redhatrussia/blog/451090/

Dockerfile reference
Best practices for writing Dockerfiles

Understand how CMD and ENTRYPOINT interact

Both CMD and ENTRYPOINT instructions define what command gets executed when running a container. There are few rules that describe their co-operation.

Dockerfile should specify at least one of CMD or ENTRYPOINT commands
ENTRYPOINT should be defined when using the container as an executable
CMD should be used as a way of defining default arguments for an ENTRYPOINT command or for executing an ad-hoc command in a container
CMD will be overridden when running the container with alternative arguments

The table below shows what command is executed for different ENTRYPOINT / CMD combinations:

	No ENTRYPOINT	ENTRYPOINT exec_entry p1_entry	ENTRYPOINT [“exec_entry”, “p1_entry”]
No CMD	error, not allowed	/bin/sh -c exec_entry p1_entry	exec_entry p1_entry
CMD [“exec_cmd”, “p1_cmd”]	exec_cmd p1_cmd	/bin/sh -c exec_entry p1_entry	exec_entry p1_entry exec_cmd p1_cmd
CMD [“p1_cmd”, “p2_cmd”]	p1_cmd p2_cmd	/bin/sh -c exec_entry p1_entry	exec_entry p1_entry p1_cmd p2_cmd
CMD exec_cmd p1_cmd	/bin/sh -c exec_cmd p1_cmd	/bin/sh -c exec_entry p1_entry	exec_entry p1_entry /bin/sh -c exec_cmd p1_cmd

If CMD is defined from the base image, setting ENTRYPOINT will reset CMD to an empty value. In this scenario, CMD must be defined in the current image to have a value.

Gracefully Stopping Docker Containers
Gracefully Shutdown Docker Container

https://12factor.net/ru/
https://medium.com/@ruslanfg/12-факторов-для-разработки-по-a8585aaaf252

RedHatRussia Habr Blog: Red Hat Universal Base Image (UBI) строить и жить помогает
Where’s The Red Hat Universal Base Image Dockerfile
RedHat Developers blog: Red Hat Universal Base Image and Docker Hub: Why should developers care?
RedHat free Ebook: Red Hat Universal Base Images (UBI)
Crunchtools blog: All You Need To Know About Red Hat Universal Base Image

Explaining Docker Image IDs

SHA256 Digests of images only compute in manifest when you push them on Docker Registry with V2 API


[student@workstation test]$ cat Dockerfile
FROM rhel7
CMD echo test
[student@workstation test]$ docker build .
Sending build context to Docker daemon 2.048 kB
Step 1 : FROM rhel7
Trying to pull repository registry.lab.example.com:5000/rhel7 ...
latest: Pulling from registry.lab.example.com:5000/rhel7
b25889d27310: Already exists
9161239f9b22: Already exists
Digest: sha256:50e10c089959be7803c0b6dfe3de5b717c3fb4f8584bd38a90b5504f55a98821
 ---> 93bb76ddeb7a
Step 2 : CMD echo test
 ---> Running in fc7aea11aad8
 ---> b14d1cce99ee
Removing intermediate container fc7aea11aad8
Successfully built b14d1cce99ee
[student@workstation test]$ docker images --digests
REPOSITORY                                         TAG                      DIGEST                                                                    IMAGE ID            CREATED             SIZE
<none>                                             <none>                   <none>                                                                    b14d1cce99ee        8 seconds ago       192.7 MB
[student@workstation test]$ docker tag b14d1cce99ee registry.lab.example.com:5000/do180/rhel7-customimage
[student@workstation test]$ docker images --digests
REPOSITORY                                              TAG                      DIGEST                                                                    IMAGE ID            CREATED              SIZE
registry.lab.example.com:5000/do180/rhel7-customimage   latest                   <none>                                                                    b14d1cce99ee        About a minute ago   192.7 MB
[student@workstation test]$ docker push registry.lab.example.com:5000/do180/rhel7-customimage
The push refers to a repository [registry.lab.example.com:5000/do180/rhel7-customimage]
86888f0aea6d: Mounted from do288/nginx-parent
dda6e8dfdcf7: Mounted from do288/nginx-parent
latest: digest: sha256:ba9cf3994b932b1331313d04705cc6ad1314216d4a5ad34bd288857b26134a3b size: 737
[student@workstation test]$ docker images --digests
REPOSITORY                                              TAG                      DIGEST                                                                    IMAGE ID            CREATED              SIZE
registry.lab.example.com:5000/do180/rhel7-customimage   latest                   sha256:ba9cf3994b932b1331313d04705cc6ad1314216d4a5ad34bd288857b26134a3b   b14d1cce99ee        About a minute ago   192.7 MB

GitHub: docker-cli issue: docker images –digest image does not display digest. Opened bug
GitHub: moby issue: Docker build should compute image digests #32016

6. Deploying Containerized Applications on OpenShift

Openshift Docs: Getting started with the CLI

https://github.com/jamiehannaford/what-happens-when-k8s

https://kubernetes.io/ru/docs/concepts/overview/working-with-objects/kubernetes-objects/

Kubernetes hands on series: What happens when you create a Pod in Kubernetes?

Troubleshooting OpenShift SDN

Openshift SDN diagram

https://itnext.io/benchmark-results-of-kubernetes-network-plugins-cni-over-10gbit-s-network-36475925a560

oc get hostsubnet
NAME                   HOST                   HOST IP           SUBNET
rh71-os1.example.com   rh71-os1.example.com   192.168.122.46    10.1.1.0/24
rh71-os2.example.com   rh71-os2.example.com   192.168.122.18    10.1.2.0/24
rh71-os3.example.com   rh71-os3.example.com   192.168.122.202   10.1.0.0/24

The Interfaces on a Node
These are the interfaces that the OpenShift SDN creates:

br0: The OVS bridge device that containers will be attached to. OpenShift SDN also configures a set of non-subnet-specific flow rules on this bridge.

tun0: An OVS internal port (port 2 on br0).
This gets assigned the cluster subnet gateway address, and is used for external network access.
OpenShift SDN configures netfilter and routing rules
to enable access from the cluster subnet to the external network via NAT.

vxlan_sys_4789: The OVS VXLAN device (port 1 on br0), which provides access to containers on remote nodes. Referred to as vxlan0 in the OVS rules.

vethX (in the main netns): A Linux virtual ethernet peer of eth0 in the Docker netns. It will be attached to the OVS bridge on one of the other ports.

SDN Flows Inside a Node

Depending on what you are trying to access (or be accessed from) the path will vary. There are four different places the SDN connects (inside a node). They are labeled in red on the diagram above.
Pod: Traffic is going from one pod to another on the same machine (1 to a different 1)
Remote Node (or Pod): Traffic is going from a local pod to a remote node or pod in the same cluster (1 to 2)
External Machine: Traffic is going from a local pod outside the cluster (1 to 3)
Of course the opposite traffic flows are also possible.

S2I process explained

Openshift.com blogs: Enhancing your Builds on OpenShift: Chaining Builds

Youtube Video: OpenShift for Beginners - CI/CD & DevOps - Builds and Build Triggers

OpenShift 4(and 3): Image Builds

Github repo: sclorg containers doc

Using Red Hat OpenShift image streams with Kubernetes deployments

How to Simplify Container Image Management in Kubernetes with OpenShift Image Streams

Pic. 1. Image Stream python pointing to two external docker registries (tags 3.5 and 3.6), one internal registry, and to a different tag.

Using a custom builder image on Red Hat OpenShift with OpenShift Do

Sticking with HEAD on OpenShift with Image Streams

Variations on imagestreams in OpenShift 4

OpenShift Commons Briefing #43: Source-to-Image Deep Dive

https://www.openshift.com/blog/linux-capabilities-in-openshift

https://cookbook.openshift.org/

opensource.com free e-book: A guide to Kubernetes for SREs and sysadmins
E-BOOK Managing your Kubernetes clusters for dummies

https://itnext.io/4-container-design-patterns-for-kubernetes-a8593028b4cd

7. Deploying Multi-Container Applications

docker networks: bridge, overlay

8. Troubleshooting Containerized Applications

Learnk8s blog: A visual guide on troubleshooting Kubernetes deployments

OpenShift 3.11: Triaging Disasters and Outages

RedHat Article: Consolidated Troubleshooting Article OpenShift Container Platform 4.x

9. Comprehensive Review of Introduction to Containers, Kubernetes, and Red Hat OpenShift

https://www.richardwalker.dev/pages/openshift.html

https://access.redhat.com/articles/5059881
https://www.certdepot.net/openshift-articles/

https://kodekloud.com/blog/best-kubernetes-books/

https://github.com/redhat-scholars/redhat-scholars.github.io
Cloud Native workshops and tutorials

OpenShift Starter Guides Developing Java Applications on OpenShift - Starter Lab

You will find here notes and links to official docs with additional information on products and technologies that described on RedHat Cources.
THIS DOCUMENT DOES NOT REPRINT ANY COPYRIGHTED CONTENT FROM REDHAT TRAINING. You will find here only public accessible outline.

DO180 "Introduction to Containers, Kubernetes, and Red Hat OpenShift" notes in the margin

tags: red hat, openshift, docker, containers

Image Not Showing Possible Reasons The image file may be corruptedThe server hosting the image is unavailableThe image path is incorrectThe image format is not supported Learn More → Table of contents

1. Getting Started with Container Technology

2. Creating Containerized Services

3. Managing Containers

4. Managing Container Images

5. Creating Custom Container Images

6. Deploying Containerized Applications on OpenShift

7. Deploying Multi-Container Applications

8. Troubleshooting Containerized Applications

9. Comprehensive Review of Introduction to Containers, Kubernetes, and Red Hat OpenShift

Read more

RH415 "Red Hat Security: Linux in Physical, Virtual, and Cloud" notes in the margin

RH134 Red Hat System Administration II notes in the margin

RH294 "Automation with Ansible" notes in the margin

DO280 "Red Hat OpenShift Administration II: Operating a Production Kubernetes Cluster" notes in the margin

tags: `red hat, openshift, docker, containers`

Image Not Showing Possible Reasons
The image file may be corrupted
The server hosting the image is unavailable
The image path is incorrect
The image format is not supported
Learn More →

Table of contents