Containerization on August Feng

Compiling apt in a container

Fri, 14 Feb 2025 00:00:00 +0000

About

I was in the mood to debug apt so let's do it. Since I'm on a mac, I'll be using a docker container as an environment.

Install docker-tramp

The docker-tramp package will allow me to use dired with a container's file system.

Configuring the debian sources

The apt project allows to download a packages source code, we just need to enable it in the sources list.

Uncovering iptables in GKE

Tue, 30 May 2023 00:00:00 +0000

About

This is a quick walkthrough on the plumbing for routing cluster-level traffic of a private GKE cluster to the GCP managed control plane.

Walkthrough

find ip range of control plane

This is the subnet for the control plane, in a VPC from a GCP managed project. Private clusters are connected to it via a VPC Network Peering connection.

  gcloud container clusters describe ${cluster} --zone ${zone} --format json | jq '.privateClusterConfig.masterIpv4CidrBlock' # 10.0.0.0/28

find cluster ip of kube-apiserver

  kubectl -n default get svc kubernetes # 10.210.34.1

connect to a node

The first step is to connect to a node in the cluster.

Environment variables and volumes when building images with Docker Compose

Mon, 03 Apr 2023 00:00:00 +0000

About

Just a short article documenting an investigation on images built from docker compose files.

Code

Dockerfile

  FROM alpine

  CMD ["printenv", "ls -l /foobar"]

docker-compose.yaml

    services:
      foobar:
        image: helloworld
        build:
          context: .
        volumes:
        - "./foobar:/foobar"
        environment:
        - foobar=helloworld

Run

This is the output when we run docker compose up --build:

  docker-compose0-foobar-1  | foobar=helloworld
  docker-compose0-foobar-1  | HOSTNAME=207ea31f2156
  docker-compose0-foobar-1  | SHLVL=1
  docker-compose0-foobar-1  | HOME=/root
  docker-compose0-foobar-1  | PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
  docker-compose0-foobar-1  | PWD=/
  docker-compose0-foobar-1  | total 0
  docker-compose0-foobar-1  | -rw-r--r--    1 root     root             0 Apr  3 16:53 helloworld.txt
  docker-compose0-foobar-1 exited with code 0

This is the output when we run docker run -it helloworld:

Digests from Docker manifests

Sat, 17 Dec 2022 00:00:00 +0000

About

This article documents a brief study I did on docker manifests.

For a given container image, the .layers[].digest (jq) field of the Docker Image Manifest V2 is different from the .[].RootFS.Layers (jq) of the docker image inspect command or when using Alex Goodman's dive tool.

A Simple Container and Registry

For this experiment, our specimen will be a simple alpine image with a foobar.txt file added:

  docker build - -t foobar <<< "FROM alpine" <<< "RUN echo helloworld > foobar.txt"

We'll be hosting our own docker registry for this experiment and pushing our foobar there:

Vendoring helm charts for jsonnet usage

Mon, 28 Nov 2022 00:00:00 +0000

This post goes over the detail of a Makefile target which converts helm charts into a yaml file, so that it can be used as input for jsonnet.

Why ?

To manipulate the kubernetes manifests file using jsonnet instead of helm's values.yml file.

Jsonnet gives us the ability to manipulate the data using its very powerful functional DSL.

How ?

  PROMETHEUS_VERSION=14.4.0

  .PHONY: yq
  yq:
      @(yq --version | grep "version 4" ) >/dev/null 2>&1 || (echo "yq version 4 is not installed."; exit 1)

  HELM_VERSION = 3.6.2
  HELM_C := docker run \
      --rm \
      --entrypoint "" \
      alpine/helm:${HELM_VERSION} \
      /bin/sh -c

  upstream/prometheus.yaml: yq
      ${HELM_C} "( helm repo add prometheus-community https://prometheus-community.github.io/helm-charts; \
      helm repo update; \
      ) 2>&1 >/dev/null; \
      helm template \
      --release-name prometheus \
      --version ${PROMETHEUS_VERSION} \
      prometheus-community/prometheus" > upstream/prometheus.yaml

What ?

Helm provides a docker image for the ease of running helm commands in a CI/CD Pipeline.