My Blog

How To Atomically Update A Counter Shared Between Docker Instances

2017-07-18T00:00:00+03:00

Problem

There are some multiple API endpoints (REST services for example) that increased some counter every time API is called. The counter value must be shared between endpoints. They are often dockerized and different containers can be run on different hosts.

Solution

To solve given problem using for example database is overhead. Everything needed is just some distributed lightweight key-value storage with shared lock support. Here are some candidates:

How To Save Files Right

2013-01-20T00:00:00+02:00

Create temporary file. Handle all possible exceptions.
Write data to that temporary file. Handle all possible exceptions.
Close temporary file. During that exceptions are also possible.
If all previous steps completes successfully, rename temporary file to existing file and handle all possible exceptions.

Steps 1-3 can be combined together if there is a function available that creates file with given content.

Following those steps prevents a lot of failures like insufficient disk space or reset during file saving.

Static Pages In Symfony

2012-12-11T00:00:00+02:00

Almost all websites have some kind of static pages that does not need any logic. Usually they have empty controller that looks like:

<?php

public function aboutAction()
{
    return $this->render('AcmeBundle:Pages:about.html.twig');
}

You also need to reference them in the routing configuration:

about:
    pattern: /about
    defaults: _controller: 'AcmeBundle:Pages:about'

Annotations usage simplifies things but it still too much work:

<?php
/**
 * @Route("/about", name="about")
 * @Template
 */
public function aboutAction()
{
    return array();
}

Instead that you can use built-in symfony’s controller FrameworkBundle:Template:template and configure everything right in the routing configuration file:

about:
    pattern: /about
    defaults:
        _controller: FrameworkBundle:Template:template
        template: 'AcmeBundle:Pages:about.html.twig'

If You look at the controllers source You will see that it simply renders passed template using templating service:

<?php
// vendor/symfony/symfony/src/Symfony/Bundle/FrameworkBundle/Controller/TemplateController.php
class TemplateController extends ContainerAware
{
    public function templateAction($template)
    {
        return $this->container->get('templating')->renderResponse($template);
    }
}

Initial Git Configuration

2012-11-11T00:00:00+02:00

After Git is set up it is good idea to customize it.

Information to identify Yourself

me@host$ git config --global user.name "John Doe"
me@host$ git config --global user.email johndoe@example.com

Preferred editor

me@host$ git config --global core.editor nano

Diff/Merge tool

me@host$ git config --global merge.tool kdiff3

Prevent some possible problems

Defines the action git push should take if no refspec is given on the command line, no refspec is configured in the remote, and no refspec is implied by any of the options given on the command line. “Current” means push the current branch to a branch of the same name.

me@host$ git config --global push.default current

Useful configuration

Here are some useful configuration values described.

In addition to .gitignore (per-directory) and .git/info/exclude, git looks into this file for patterns of files which are not meant to be tracked. “~/” is expanded to the value of $HOME and “~user/” to the specified user’s home directory

me@host$ git config --global core.excludesfile <path to file>

Specify a file to use as the template for new commit messages. “~/” is expanded to the value of $HOME and “~user/” to the specified user’s home directory.

me@host$ git config --global commit.template <path to file>

Useful commands

Here are some useful commands described

Displaying console graph log

me@host$ git log --oneline --graph --decorate

Show a word diff highlighting changed words using only colors

me@host$ git diff --word-diff=color