DEV Community: Arash Hatami

4 common reasons cron jobs fail

Arash Hatami — Tue, 15 Mar 2022 09:36:02 +0000

Cron job failures create chaos for your users and your team. These 4 problems emerged as the most likely causes of preventable job failures:

1. System resources have been depleted

Without careful cleanup and log rotation, system resources like disk space can be consumed slowly over months or years before leading to job failures. By carefully cleaning up any files your cron job creates and using a tool like logrotate to automatically prune log files you can prevent disk space related failures.

Other resource problems, especially when running cron jobs in a virtual machine, are limits to the number of open file descriptors, threads, and memory usage. You can view limits on your system by running ulimit -a as the cron user.

2. Recent infrastructure updates were made

When developers are making changes to database connections or upstream APIs it's easy to overlook cron jobs, especially when they're running on a separate host. It can help if cron jobs are deployed like the rest of your app and are included in post-release verification steps.

3. Your dataset has grown too large

Cron jobs are often used for batch processing, event sourcing and other data intensive tasks that can reveal the constraints of your stack. Jobs may work fine until your data size grows to a point where a bottleneck is reached.

Optimizing database queries and API calls is the right place to start, and depending on the job, running it more frequently may be effective by reducing the data processed each time it runs.

4. Cron job invocations begin to overlap

Cron will run your command at the scheduled time even if the last invocation is still running, or even if the last 10 are. If your job invocations are close to overlapping, consider spacing them out further or adding a tool like flock to ensure only 1 instance is running.

How to launch Jekyll project in VS Code

Arash Hatami — Sun, 12 Dec 2021 12:56:20 +0000

There is many extensions and multiple ways to run/launch/debug a project using a simple F5 key! I always developed web projects with Jetbrains PHPStorm, But last week I had to do this with VSCode and the first thing I encountered was the simple execution of the Jekyll project.

You can simply run the whole project with this command :

bundle exec Jekyll serve

But how can we execute this command with the F5 key? This is where it gets a little annoying. VSCode can debug projects when a supported extension installed and the problem is that Jekyll extensions can not run/debug project.

With a little effort and testing different ways, I found the best way to do that. We can combine Task and Launch configuration.

1- Create tasks.json in .vscode folder like this:

{
  "version": "2.0.0",
  "tasks": [
    {
      "label": "jekyll",
      "command": "bundle exec jekyll serve",
      "type": "shell"
    }
  ]
}

This task will run the command for us.

2- Create launch.json file like this:

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "firefox",
      "request": "attach",
      "name": "Attach",
      "preLaunchTask": "jekyll"
    }
  ]
}

We use Firefox launch configuration to open our browser, and also run a preLaunchTask before that!

Now you debug your project and open Firefox automatically by press the lovely F5 key 🤩

Scan Docker images using Trivy

Arash Hatami — Wed, 01 Dec 2021 14:22:50 +0000

My Workflow

Docker is currently one of the main tools in the DevOps domain. You may be dealing with multiple Docker Images every day. Certainly.
In the past, I used to create and publish Docker Images manually on my own PC, Now with Github Actions, my affairs are very fast and easy and I leave everything to Github.

For example look at my repository (Memcached-Admin). It's a Dockerized PHP web application to manage Memcached server(s). I should pass these steps to use this project :

Build Image
Check and scan security vulnerabilities
Push to Dockerhub
Push to Other Docker registries

Doing these things normally will waste my time, also after planning the necessary things to build the image, it's necessary to ensure their security and the absence of security bugs. Here we have one of the best tools ... Trivy 💪. A Simple and Comprehensive Vulnerability Scanner for Containers and other Artifacts, Suitable for CI.

Thanks to Github Action, now we can have all things together.

I wrote simple workflows to handle the whole process.

hatamiarash7 / Memcached-Admin

Memcached admin for docker

Memcached Admin

This program allows to see in real-time (top-like) or from the start of the server, stats for get, set, delete, increment, decrement, evictions, reclaimed, cas command, as well as server stats (network, items, server version) with google charts and server internal configuration

You can go further to see each server slabs, occupation, memory wasted and items (key & value).

Another part can execute commands to any memcached server : get, set, delete, flush_all, as well as execute any commands (like stats) with telnet

Statistics

Stats for each or all memcached servers, items, evicted, reclaimed ...
Stats for every command : set, get, delete, incr, decr, cas ...
Slabs stats (Memory, pages, memory wasted, items)
Items stats (View items in slabs, then data for each key)
Network stats (Traffic, bandwidth)

Commands

Execute commands : get, set, delete, flush_all on servers to administrate or debug it
Get…

View on GitHub

Submission Category:

Maintainer Must-Haves

Yaml File or Link to Code

name: Docker Image CI

on:
  push:
    branches: [master]
  pull_request:
    branches: [master]

jobs:
  build:
    name: Build
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v2

      - name: Build the Docker image
        run: docker build -t memcached-admin:${{ github.sha }} .

      - name: Run Trivy vulnerability scanner
        uses: aquasecurity/trivy-action@master
        with:
          image-ref: "memcached-admin:${{ github.sha }}"
          exit-code: "1"
          ignore-unfixed: true
          vuln-type: "os,library"
          severity: "CRITICAL,HIGH"
          format: "template"
          template: "@/contrib/sarif.tpl"
          output: "trivy-results.sarif"

      - name: Upload Trivy scan results to GitHub Security tab
        uses: github/codeql-action/upload-sarif@v1
        with:
          sarif_file: "trivy-results.sarif"

This workflow has 4 simple step:

Checkout my code
Build Docker image
Scan using Trivy
Upload results to GitHub Code scanning

I can see results in Security tab of my project:

Now i can push my image to Dockerhub using another workflow:

name: Publish Dockerhub

on:
  schedule:
    - cron: "0 2 * * *"
  push:
    branches: [master]
  pull_request:
    branches: [master]

env:
  REGISTRY: docker.io
  IMAGE_NAME: hatamiarash7/memcached-admin

jobs:
  build:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      packages: write

    steps:
      - name: Checkout repository
        uses: actions/checkout@v2

      - name: Log into registry ${{ env.REGISTRY }}
        if: github.event_name != 'pull_request'
        uses: docker/login-action@28218f9b04b4f3f62068d7b6ce6ca5b26e35336c
        with:
          registry: ${{ env.REGISTRY }}
          username: ${{ github.actor }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}

      - name: Extract Docker metadata
        id: meta
        uses: docker/metadata-action@98669ae865ea3cffbcbaa878cf57c20bbf1c6c38
        with:
          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}

      - name: Build and push Docker image
        uses: docker/build-push-action@ad44023a93711e3deb337508980b4b5e9bcdc5dc
        with:
          context: .
          push: ${{ github.event_name != 'pull_request' }}
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}

Another amazing feature about Github Action is that I can schedule to run my workflow. For example push image at 02:00 every day:

...

on:
  schedule:
    - cron: "0 2 * * *"

...

Now everything will be done automatically and I just need to push the changes to the repository 😍

Additional Resources / Info

I used this action: aquasecurity/trivy-action