Kind - local k8s

Sun 13 September 2020 by admin

Few words after using kind:

  • works only with docker, there is also a podman provider (not tested)
  • docker image node-image simulates a k8s node - all components in one image, started by systemd
  • docker container is priviledged
  • easy to start just use kind command, under the hood it download right node-image version and start it
  • node-image is based on base-image
  • you can run multiple node cluster
  • you can customize kind configuration ie. number/types of nodes, exposed ports to host, extra mounts, kubeadm patches
  • when you customize kubeadm section, kind on boot apply those changes
  • kind container is bound to docker network driver bridge
  • kind ships with simple CNI kindnet and it's also swappable
  • CRI is implemented by containerd
  • kind is using internal image registry
  • hard to expose services when running MacOSX, Windows, easier to expose services as k8s ingress
  • good for testing, because of fast start
  • not fully featured as minikube
  • cannot easily simulate cluster upgrade

Custom node condition in Kubernetes

Sun 30 August 2020 by admin

When you go through node object in k8s you can see that there is a field called Conditions:

$ kubectl describe node kind-control-plane
...
Conditions:
  Type              Status  LastHeartbeatTime                 LastTransitionTime                Reason                       Message
  ----              ------  -----------------                 ------------------                ------                       -------
  MemoryPressure    False   Sun, 30 Aug 2020 10:54:31 +0200   Sun, 30 Aug 2020 10:53:23 +0200   KubeletHasSufficientMemory   kubelet has ...
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ICMP Echo permissions

Sun 23 August 2020 by admin

Network ping tool, one of the most widely used tool to debug network problem. It's mainly using ICMP protocol, due to specific security requirements to send/receive ICMP ECHO packets regular user is not allowed to use it. How can dealt with it on linux box ?

  • the easiest way ...
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gRPCurl - curl for gRPC

Sun 26 July 2020 by admin

In previous blog post How kubernetes is interacting with docker ? I was writing about dockershim with golang gRPC example code to get list of docker images. This example was trivial but writing code to get it wasn't trival, is there any generic tool to make such requests ? In HTTP ...

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CNI - the Container Network Interface

Sat 04 July 2020 by admin

CNI is simple interface based on environment variables and JSON config. Both environment variables and JSON config are processed by CNI plugin started by container management system like Kubernetes. CNI plugin is responsible for connecting container namespace into selected network, second responsibility for CNI is to provide IP address it ...

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Docker and Kubernetes at network layer

Sun 21 June 2020 by admin

I wrote some posts about how kubernetes is interacting with docker at CRI level, but what about networking ? Docker has developed it's own solution called CNM to maintain network, to interact with it just use commands under docker network. How it looks like in k8s multi node environment:

# docker ...
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dropwatch - discover where network packets are dropped

Sat 30 May 2020 by admin

Let's imagine situation where you experience network problem with dropping packets and you've no idea where the problem is located. So first of all prepare environment:

# iptables -A OUTPUT -p icmp -j DROP
# ping -c 3 -W 1 8.8.8.8
PING 8.8.8.8 (8 ...
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mkubectx - single command across all your selected kubernetes contexts

Sun 10 May 2020 by admin

Pause - most popular container in k8s environment

Sat 02 May 2020 by admin

Probably the most popular container in kubernetes environment. Container image is really small:

$ docker images | grep -i pause
k8s.gcr.io/pause                          3.2                 80d28bedfe5d        2 months ago        683kB

Codebase is also small pause. According to source code it is responsible for doing pretty... nothing, except of dealing ...

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How to change default k8s container runtime to containerd ?

Sun 26 April 2020 by admin

Default kubelet container runtime configuration use docker as CRI. Containerd has another implementation of CRI, it should fullfill the same requirements as docker so ie. it's responsible to maintain container images. Containerd extends its functionality by using plugins, one of them is cri. To interact with containerd we can ...

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