Category Archives for computers

Watch files and execute command upon change

Find yourself executing the same command over and over again after applying changes to certain files? Pywatch will be you best friend!

Meet pywatch: a cool little app that watches directories and files. Whenever it finds a file that changed, it executes the command you provided.


As an example; I use this to build a Docker image whenever I save a change to my Dockerfile.

pywatch "docker build . -t pauledenburg/behat" Dockerfile

Or execute tests whenever I make a change to one of the sourcefiles.

commandToExecute='docker exec -i hangman_app_1 behat -c tests/behat/behat.yml'
find ./tests -name "*.php" -o -name "*.feature" \
  | xargs pywatch "$commandToExecute"

This keeps an eye on all *.php and *.feature files under ./tests.

When one of these files changes, it executes $commandToExecute which resolves to executing behat in a Docker container.


Download the pywatch app from github:

Then unzip and install with python.

cd pywatch-master
sudo python install

Advanced usage

Nice one: run tests when files change and create a Mac notifier whenever the tests fail.

This way you can keep the tests running in the background and you’ll be notified whenever a test failed.

find src tests -name "*.php" -o -name "*.feature" \
  | xargs pywatch "./dev test phpunit" \
  | grep "([0-9]* failed)" \
  | sed -e 's/.*(\([0-9]* failed\)).*/\1/' \
  | while read failure; 
      terminal-notifier -message "Test output: $failure" -title "Tests Failed!"



Set up NGINX as a proxy for your Docker containers

Recently I’m a fan of serving docker containers over serving Virtual Hosts using a webserver.

In order to use regular domainnames without ports, I set up Nginx to receive the request on the domainname and let it forward the request to the relevant Docker container on the specific port it is running on.


Imagine I have a Docker webserver-container hosting my app. It runs on my server exposing port 8080. I use the URL

I don’t want people to use but just the URL without the port


I use nginx for this:

server {
    listen 80;

    location / {
        proxy_pass http://localhost:8080;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;

And now add SSL to it 🙂

Complete ELK-stack example with Docker

I wanted a quick setup for an Elasticsearch Logstach and Kibana (ELK-)stack to work with. But searching on the internet gave me too many long-winded not really working examples.

That’s why I created this page. Use it to quickly get up-and-running with an ELK-stack of your own.

Create the file docker-compose.yml

# file: docker-compose.yml
version: "3"

    image: sebp/elk
      - "5601:5601"
      - "9200:9200"
      - "5044:5044"
      - MAX_MAP_COUNT=262145
      - KIBANA_START=1
      - TZ="Europe/Amsterdam"
      - elk-data:/var/lib/elasticsearch


Now start up with docker-compose up -d. That’s it!

5601: endpoint for Kibana
9200: endpoint for elastic search

Add some security

Don’t leave your elastic-search open for everyone.

Add some basic security by adding a .htpasswd config to your webserver.

$ sudo sh -c "echo -n 'myelasticuser:' >> /etc/nginx/.htpasswd"
$ sudo sh -c "openssl passwd -apr1 >> /etc/nginx/.htpasswd"
Verifying - Password:

Add it to your webserver, like nginx.

server {
    listen 80 default_server;
    listen [::]:80 default_server ipv6only=on;

    root /var/www/html;
    index index.html index.htm;

    server_name localhost;

    location / {
        try_files $uri $uri/ =404;
        auth_basic "Restricted Content";
        auth_basic_user_file /etc/nginx/.htpasswd;

Reload nginx.

$ sudo nginx -t
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

$ sudo service nginx reload

Some notes

I chose the Docker image of sebp because he’s got great documentation. Go check it out!

Especially the part with the Frequently Encountered Issues.

There, you’ll see that you’ll:

  • need 4GB of memory for the Docker container
  • need to set the amount of virtual memory on linux by setting the max map count:sudo sysctl -w vm.max_map_count=262144

Free SSL certificates with LetsEncrypt

Getting your website on https can be done in a matter of minutes. So there is no excuse anymore to go without it. Not even on your test and dev websites.

As this example is on CentOS, it really goes for any other linux distro.

Excellent, tailor-made instructions per webserver and OS are found on the website of Certbot:

Here, a short recap of that for my own archive.

You’ll need the repel repository for this. After that, install the certbot software.

$ sudo yum install epel-release
$ sudo yum install certbot-nginx


Getting your website secured with SSL is now as simple as answering some questions on the following command.

Note: I’m using a method which takes a bit of downtime because LetsEncrypt is in the middle of an update. Read all about it

$ sudo certbot --authenticator standalone --installer nginx --pre-hook "service nginx stop" --post-hook "service nginx start"

Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator standalone, Installer nginx
Which names would you like to activate HTTPS for?
Select the appropriate numbers separated by commas and/or spaces, or leave input
blank to select all options shown (Enter 'c' to cancel): 2

Running pre-hook command: service nginx stop
Error output from service:
Redirecting to /bin/systemctl stop nginx.service
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for
Waiting for verification...
Cleaning up challenges
Running post-hook command: service nginx start
Error output from service:
Redirecting to /bin/systemctl start nginx.service
Deployed Certificate to VirtualHost /etc/nginx/sites-enabled/ for set([''])
Please choose whether or not to redirect HTTP traffic to HTTPS, removing HTTP access.
1: No redirect - Make no further changes to the webserver configuration.
2: Redirect - Make all requests redirect to secure HTTPS access. Choose this for
new sites, or if you're confident your site works on HTTPS. You can undo this
change by editing your web server's configuration.
Select the appropriate number [1-2] then [enter] (press 'c' to cancel): 2
Redirecting all traffic on port 80 to ssl in /etc/nginx/sites-enabled/
Congratulations! You have successfully enabled
You should test your configuration at:
 - Congratulations! Your certificate and chain have been saved at:
   Your key file has been saved at:
   Your cert will expire on 2018-04-24. To obtain a new or tweaked
   version of this certificate in the future, simply run certbot again
   with the "certonly" option. To non-interactively renew *all* of
   your certificates, run "certbot renew"
 - If you like Certbot, please consider supporting our work by:
   Donating to ISRG / Let's Encrypt:
   Donating to EFF:          


Things which might throw you an error

python-urllib3 version

First caveat for CentOS7 is that you need specific version 1.21 for urllib3. I had 1.22 installed via yum which gave me the following error.

ImportError: No module named 'requests.packages.urllib3'

You can see the currently installed version with pip:

pip freeze | grep urllib

To resolve this, first remove the old version it with yum and then add it with pip:

sudo yum remove python-urllib3 
sudo pip install -Iv

pyOpenSSL version

Just like urllib3, pyOpenSSL was of an unsupported version.

sudo yum remove pyOpenSSL
sudo pip install pyOpenSSL

Error message stating that the CA can’t be satisfied

After running

certbot --nginx

you get the following error:

Client with the currently selected authenticator does not support any combination of challenges that will satisfy the CA.

Due to legal reasons there currently is no

From the github certbot website:

If you’re serving files for that domain out of a directory on Nginx, you can run the following command:

# Webroot method
$ sudo certbot --authenticator webroot --installer nginx \
  --webroot-path <path to served directory> -d <domain>

If you’re not serving files out of a directory (for instance if you are using proxy_pass), you can temporarily stop your server while you obtain the certificate and restart it after Certbot has obtained the certificate. This would look like:

# Temporary outage method
$ sudo certbot --authenticator standalone --installer nginx \
  -d <domain> --pre-hook "service nginx stop" --post-hook "service nginx start"


SonarQube with Postgres on docker-compose

[updated 2022-08-08]

Struggling to get a working environment with SonarQube and PostgreSQL?

Use the following docker-compose file and be up and running in minutes.

It is as ‘bare’ as possible:

  • use of official Docker images for both PostgreSQL and SonarQube
  • no other configuration required
  • use of volumes so you can backup your data

Recommended system specs

  • >= 3GB of RAM
# file: docker-compose.yml

version: "3"

    image: sonarqube:9-community
    # platform: linux/amd64  # uncomment this when using Mac M1
    restart: unless-stopped
      - SONARQUBE_JDBC_URL=jdbc:postgresql://db:5432/sonarqube
      - "9000:9000"
      - "9092:9092"
      - sonarqube_conf:/opt/sonarqube/conf
      - sonarqube_data:/opt/sonarqube/data
      - sonarqube_extensions:/opt/sonarqube/extensions
      - sonarqube_bundled-plugins:/opt/sonarqube/lib/bundled-plugins

    image: postgres:14.4
    # platform: linux/amd64  # uncomment this when using Mac M1
    restart: unless-stopped
      - POSTGRES_USER=sonar
      - POSTGRES_DB=sonarqube
      - sonarqube_db:/var/lib/postgresql
      # This needs explicit mapping due to
      - postgresql_data:/var/lib/postgresql/data


Start this stack with the following command:

# start the containers
docker-compose up -d

You can reach your SonarQube instance at http://localhost:9000

Use the default credentials admin/admin to login.

Useful links:

Ansible stat module

I use the Ansible stat module mostly for conditional statements.

For example, only when directory /var/www/phpmyadmin does not exist include the task for installing PHPMyAdmin.

Only when <directory> exists; <do this>

But of course, there are a lot of other uses for this module then the one I use most.

It does this by doing the following two things:

  1. get all system-information about the directory
  2. execute statement, depending on values from the fetched system-information

But there are a lot of uses for the stat module.

The official documentation for the stat module is on, ofcourse, the Ansible website:

full example

# file: install.yml

# install PHPMyAdmin when it's not installed already
- name: PHPMyAdmin | check the need for installment
    path: /var/www/html/phpmyadmin
  register: pma

# Only include the PHPMyAdmin installation-task when it's not installed yet
# e.g. the directory /var/www/html/phpmyadmin does not exist
- include: PHPMyAdmin | install
  when: pma.stat.isdir is not defined

As you can see, we’re checking against the variable pma which holds the stats information for our path /var/www/html/phpmyadmin. This variable holds a lot more then just the isdir property.

The full list of information returned by the Ansible stat module:

  • atime
  • attributes
  • charset
  • checksum
  • ctime
  • dev
  • executable
  • exists
  • gid
  • gr_name
  • inode
  • isblk
  • ischr
  • isdir
  • isfifo
  • isgid
  • islnk
  • isreg
  • issock
  • isuid
  • lnk_source
  • md5
  • mime_type
  • mode
  • mtime
  • nlink
  • path
  • pw_name
  • readable
  • rgrp
  • roth
  • rusr
  • size
  • uid
  • wgrp
  • woth
  • writeable
  • wusr
  • xgrp
  • xoth
  • xusr

I will continue to update this page as needed.