MySQL backend for CoreDNS

mysql - MySQL backend for CoreDNS

This plugin uses MySQL as a backend to store DNS records. These will then can served by CoreDNS. The backend uses a simple, single table data structure that can be shared by other systems to add and remove records from the DNS server. As there is no state stored in the plugin, the service can be scaled out by spinning multiple instances of CoreDNS backed by the same database.

mysql {
    dsn DSN
    [table_prefix TABLE_PREFIX]
    [max_lifetime MAX_LIFETIME]
    [max_open_connections MAX_OPEN_CONNECTIONS]
    [max_idle_connections MAX_IDLE_CONNECTIONS]
    [ttl DEFAULT_TTL]
    [zone_update_interval ZONE_UPDATE_INTERVAL]
}

• dsn DSN for MySQL as per https://github.com/go-sql-driver/mysql examples. You can use $ENV_NAME format in the DSN, and it will be replaced with the environment variable value.
• table_prefix Prefix for the MySQL tables. Defaults to coredns_.
• max_lifetime Duration (in Golang format) for a SQL connection. Default is 1 minute.
• max_open_connections Maximum number of open connections to the database server. Default is 10.
• max_idle_connections Maximum number of idle connections in the database connection pool. Default is 10.
• ttl Default TTL for records without a specified TTL in seconds. Default is 360 (seconds)
• zone_update_interval Maximum time interval between loading all the zones from the database. Default is 10 minutes.

A, AAAA, CNAME, SOA, TXT, NS, MX, CAA and SRV. Wildcard records are supported as well. This backend doesn't support AXFR requests.

Add this as an external plugin in plugin.cfg file:

mysql:github.com/cloud66-oss/coredns_mysql

then run

$ go generate
$ go build

Add any required modules to CoreDNS code as prompted.

This plugin doesn't create or migrate database schema for its use yet. To create the database and tables, use the following table structure (note the table name prefix):

CREATE TABLE `coredns_records` (
    `id` INT NOT NULL AUTO_INCREMENT,
	`zone` VARCHAR(255) NOT NULL,
	`name` VARCHAR(255) NOT NULL,
	`ttl` INT DEFAULT NULL,
	`content` TEXT,
	`record_type` VARCHAR(255) NOT NULL,
	PRIMARY KEY (`id`)
) ENGINE = INNODB AUTO_INCREMENT = 6 DEFAULT CHARSET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci;

Each record served by this plugin, should belong to the zone it is allowed to server by CoreDNS. Here are some examples:

-- Insert batch #1
INSERT INTO coredns_records (zone, name, ttl, content, record_type) VALUES
('example.org.', 'foo', 30, '{"ip": "1.1.1.1"}', 'A'),
('example.org.', 'foo', '60', '{"ip": "1.1.1.0"}', 'A'),
('example.org.', 'foo', 30, '{"text": "hello"}', 'TXT'),
('example.org.', 'foo', 30, '{"host" : "foo.example.org.","priority" : 10}', 'MX');

These can be queries using dig like this:

$ dig A MX foo.example.org 

This plugin, is inspired by https://github.com/wenerme/coredns-pdsql and https://github.com/arvancloud/redis

To develop this plugin further, make sure you can compile CoreDNS locally and get this repo (go get github.com/cloud66-oss/coredns_mysql). You can switch the CoreDNS mod file to look for the plugin code locally while you're developing it:

Put replace github.com/cloud66-oss/coredns_mysql => LOCAL_PATH_TO_THE_SOURCE_CODE at the end of the go.mod file in CoreDNS code.

Pull requests and bug reports are welcome!