dev-replica

Pair of Docker images for Apache2 Webserver and MySQL as a read-replica against a remote master.

Requirements:

• Docker
• Terminal/CLI skills
• Further details for Webserver Config

Setup / Config:

• git clone https://github.com/Wier-Stewart/dev-replica.git
• Rename webserver.sample to webserver.env and fill in the info.
• Rename mysql_slave.sample to mysql_slave.env and fill in the info.
• Edit docker-compose.yml file: set the volumes line that looks like this ~/domains/:/var/www/domains to fit the pattern: /local-path/on-mac/to-domains/:/var/www/domains
• Set your /etc/hosts to be 127.0.0.1 local.domain.com. If you're on a Mac, this is easier: Gasmask.

Build and Run the Docker Containers:

Build only needs to happen once (usually). See "Docker Lifecycle Commands" at the end for the full commands.

$ docker-compose build
$ docker-compose up

Server Info

Once docker-compose up is up:

• The site local.domain.com should be available.
• The database should be accessible via 127.0.0.1 (not localhost oddly) on port 3306 from your Mac.
• The database will be accessible via mysql_slave from the webserver

E.g., your wp-config.php file would have a line like this:

 define('DB_HOST', 'mysql_slave');

Wordpress Integration (Per-Project)

The goal is to have all database-reads go to mysql_slave locally, and all database-writes go to the remote master db. For this, WordPress requires HyperDB.

It's not a normal plugin installation, and really only requires 2 files:

./db-config.php

Here's a mini version that will work with the usual wp-config.php variables:

<?php
//./db-config.php
$wpdb->save_queries = true;
$wpdb->persistent = false;
$wpdb->max_connections = 10;
$wpdb->check_tcp_responsiveness = true;
//replicate on local.domain.com only

if( defined( "WP_CLI" ) && WP_CLI ){
    //don't say anything, it can mess with output parsing!
}else if(stripos($_SERVER['HTTP_HOST'], 'local.')!==false ){ //replicate if local, only, not dev or preview
    $wpdb->add_database(array(
        "host"     => "mysql_slave",     // If port is other than 3306, use host:port.
        "user"     => DB_USER,
        "password" => DB_PASSWORD,
        "name"     => DB_NAME,
        "write"    => 0,
        "read"     => 1,        // replication_ok() here is preferred.
        "dataset"  => "global",
        "timeout"  => 0.5,
    ));
}

$wpdb->add_database(array(
	"host"     => DB_HOST,     // If port is other than 3306, use host:port.
	"user"     => DB_USER,
	"password" => DB_PASSWORD,
	"name"     => DB_NAME,
	"write"    => 1,
	"read"     => 1,
	"dataset"  => "global",
	"timeout"  => .9,
));

wp-content/db.php

save this to ./wp-content/db.php

Docker Lifecycle Commands:

To Start the Environment the First Time

$ docker-compose build
$ docker-compose up

To Start and Stop the Environment

$ docker-compose up
$ docker-compose stop

To Clear the Environment - will need to build after this

$ docker-compose stop
Stopping webserver   ... done
Stopping mysql_slave ... done

$ docker rm webserver

$ docker rm mysql_slave

$ docker volume prune
WARNING! This will remove all volumes not used by at least one container.
Are you sure you want to continue? [y/N] y