Killercoda Cka by Alexis Carbillet

- 8 mins read

CKA Preparation

1. CKA Practice: ConfigMaps and Secrets

  1. Create a ConfigMap and Secret
  • Your application needs a database configuration and a password stored securely.
    • Create a ConfigMap named app-config with:
      • DB_HOST=localhost
      • DB_PORT=3306
    • Create a Secret named db-secret with:
      • DB_PASSWORD=supersecret (base64 encoded automatically by kubectl)
#configmap
apiVersion: v1
kind: ConfigMap
metadata:
    name: app-config
data:
    DB_HOST: "localhost"
    DB_PORT: "3306"
#secret
apiVersion: v1
kind: Secret
metadata:
    name: db-secret
data:
    DB_PASSWORD: "c3VwZXJzZWNyZXQK" #base64 encoded value 'supersecret'
  1. Use ConfigMap and Secret in a Pod
  • Create a Pod named app-pod using the nginx image.
  • Inject the ConfigMap values as environment variables.
  • Inject the Secret value as an environment variable.
apiVersion: v1
kind: Pod
metadata:
  name: app-pod
spec: 
  containers: 
  - name: app-pod
    image: nginx
    env:
      - name: DB_HOST
        valueFrom:
          configMapKeyRef:
            name: app-config
            key: DB_HOST
      - name: DB_PORT
        valueFrom:
          configMapKeyRef:
            name: app-config
            key: DB_PORT
      - name: DB_SECRET
        valueFrom:
          secretKeyRef:
            name: db-secret
            key: DB_PASSWORD

- Lesson learned

controlplane:/var/log$ k get pods    
NAME      READY   STATUS                       RESTARTS   AGE
app-pod   0/1     CreateContainerConfigError   0          4m43s

for debugging this error ‘CreateContainerConfigError’ by using k describe pod app-pod

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Killercode Cka by Kim Wüstkamp

- 7 mins read

CKA Preparation

1. Playground

This playground will always have the same version as currently in the Linux Foundation Exam.

2. Vim Setup

Using vim to edit file

3. Apiserver Crash

Configure a wrong argument

knowledge

  • Check log
    • /var/log/pods
    • /var/log/containers
    • crictl ps + crictl logs
    • docker ps + docker logs
    • kubelet logs: /var/log/syslog or journalctl
  • kube api manifest directory
    • /etc/kubernetes/manifest/*

Solution

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Crypto Zombies

- 1 min read

Making the Zombie Factory

Event (event & emit) notificaiton trigger for front-end app, gas related that receving information/data without interacting to the contract

Zombies Attack Their Vicitms

mapping (address => uint) public accountBalance; | mapping (key => value) public accountBalance;

storage vs memory | hardisk vs ram

internal vs external vs public vs private

Advanced Solidity Concepts

OpenZeppelin ownable (modifier onlyOwner)

struct{ uint c; uint32 a; uint32 b;) gas < struct{ uint32 a; uint c; uint32 b;) gas

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Nas Docker Rss Subscription Service

- 2 mins read

For me, Freshrss is better.

I plan to test them one by one, but stop at Freshrss as I’m satisfied with it.

Planned testing sequence in order: Miniflux -> Freshrss -> Tiny tiny rss

My requirement:

  • Subscribe > 100 feeds
  • Use on PC & mobile
  • Feeds are manageable (feeds with error, remove feeds)

Comparison:

  • Miniflux

    • can suscribe >100 feeds
    • Easy to use on both PC & mobile

  • Freshrss

    • can subscribe >100 feeds
    • Easy to use on both PC & mobile
    • Better subscription mangement (e.g. remove number of feeds without click them 1 by 1)
    • Better GUI

Docker-compose

Freshrss

version: "2.4"

volumes:
  db:
  data:
  extensions:

services:
  freshrss:
    image: freshrss/freshrss:latest
    container_name: freshrss
    hostname: freshrss
    restart: unless-stopped
    logging:
      options:
        max-size: 10m
    volumes:
      - data:/var/www/FreshRSS/data
      - extensions:/var/www/FreshRSS/extensions
    environment:
      TZ: Asia/Hong_Kong
      CRON_MIN: '3'
      TRUSTED_PROXY: 0
    ports:
        - "8080:80"
    
  freshrss-db:
    image: postgres:16
    container_name: freshrss-db
    hostname: freshrss-db
    restart: unless-stopped
    logging:
      options:
        max-size: 10m
    volumes:
      - db:/var/lib/postgresql/data
    environment:
      POSTGRES_DB: freshrss-db
      POSTGRES_USER: freshrssuser
      POSTGRES_PASSWORD: freshrsspassword
    command:
      # Examples of PostgreSQL tuning.
      # https://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server
      # When in doubt, skip and stick to default PostgreSQL settings.
      - -c
      - shared_buffers=1GB
      - -c
      - work_mem=32MB

miniflux

version: '3'
services:
  miniflux:
    image: miniflux/miniflux:latest
    ports:
      - "8756:8080"
    depends_on:
      db:
        condition: service_healthy
    environment:
      - DATABASE_URL=postgres://miniflux:miniflux@db/miniflux?sslmode=disable
      - RUN_MIGRATIONS=1
      - CREATE_ADMIN=1
      - ADMIN_USERNAME=admin
      - ADMIN_PASSWORD=password
  db:
    image: postgres:15
    environment:
      - POSTGRES_USER=miniflux
      - POSTGRES_PASSWORD=miniflux
    volumes:
      - miniflux-db:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD", "pg_isready", "-U", "miniflux"]
      interval: 10s
      start_period: 30s
volumes:
  miniflux-db:

Ethernaut

- 11 mins read

Study Material

Ethernaut, a CTF-like smart contract security challenge writeup

1. Ethernaut0 - Hello Ethernaut

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract Instance {

  string public password;
  uint8 public infoNum = 42;
  string public theMethodName = 'The method name is method7123949.';
  bool private cleared = false;

  // constructor
  constructor(string memory _password) {
    password = _password;
  }

  function info() public pure returns (string memory) {
    return 'You will find what you need in info1().';
  }

  function info1() public pure returns (string memory) {
    return 'Try info2(), but with "hello" as a parameter.';
  }

  function info2(string memory param) public pure returns (string memory) {
    if(keccak256(abi.encodePacked(param)) == keccak256(abi.encodePacked('hello'))) {
      return 'The property infoNum holds the number of the next info method to call.';
    }
    return 'Wrong parameter.';
  }

  function info42() public pure returns (string memory) {
    return 'theMethodName is the name of the next method.';
  }

  function method7123949() public pure returns (string memory) {
    return 'If you know the password, submit it to authenticate().';
  }

  function authenticate(string memory passkey) public {
    if(keccak256(abi.encodePacked(passkey)) == keccak256(abi.encodePacked(password))) {
      cleared = true;
    }
  }

  function getCleared() public view returns (bool) {
    return cleared;
  }
}

1.1 Solution

Starting from contract.info() which redirecting me to a function that change “cleared” to true;

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