ssannaqvi / dnsbridge

DNS to Docker Bridge

dnsbridge

Build Requirements

Obtaining this code or updates to it may require the Git package manager. It can be installed on Fedora/RH with this command:

yum install -y git

The main requirements to build and use this software require root access, and for RHEL7 Linux this setup script will do all of them:

./requirements.sh

Installation

this install script assumes the following:

• IP address of 192.168.56.103 for this server
• Domain name of crunchy.lab
• Host name of ns.crunchy.lab
• you will be installing under your userid, not root
• your userid has sudo priviledge

You should change the IP address, hostname, and domain name to suit your local requirements. You will need to edit some of the installed scripts/files as specified below.

Before running this script you will need to:

• set up a static ip address on the installation host

• set up a hostname using the domain name of your choosing (e.g. ns.crunchy.lab)

• edit this script, add any extra remote servers that will be used as dnsbridge clients, look for 'remoteservers' at the end of this script, add any extra servers within the parens, by default, the script will include the dnsbridge server as the only remote server, this allows this server to be used as a CPM deployment server as well as a DNS server

• edit ./config/zonefiles and alter the ip addresses/domain name, and number of zones for your configuration

• edit ./config/named.conf and edit the ip address/domain names of the dnsbridge server for your configuration

• edit ./bin/add-host.sh and ./bin/delete-host.sh change domain names if required for your installation

• edit /etc/hosts and add your hostname and IP address, add an entry for the hostname that you have chosen for this server and which is specified in the installation files (e.g. ns.crunchy.lab)

• edit /etc/resolv.conf and add your IP address as the primary nameserver

• run the install.sh script

• modify /etc/sysconfig/docker to add the DNS server to Docker's list of DNS servers to use, your /etc/sysconfig/docker file should look like this:

  OPTIONS=--selinux-enabled --dns=192.168.56.103 --dns=192.168.0.1 -H fd://
  

  Adjust these DNS server IP addresses to match your environment, these values need to be correct in order to build the CPM Docker images during a CPM intallation.

  Restart Docker after making these changes.

• test the install! See Below for details on testing

Details

dnsbridge is a docker-to-DNS bridge system used for registering Docker events with a BIND system.

This is useful because IP addresses are dynamically assigned by Docker and some applications require a persistent way of locating a service, (e.g. Postgresql).

Some PaaS environments provide something akin to dnsbridge, but using dnsbridge allows for standalone deployments of some PaaS/DaaS types of applications (e.g. Crunchy PostgreSQL Manager).

dnsbridgeclient

The client is run on each Docker host, it connects to the Docker event stream, listens for start/stop/destroy messages, and when received, it forwards them to the dnsbridgeserver.

dnsbridgeserver

The server receives events (start, stop, destroy) messages from the dnsbridgeclients.

Upon receiving an event, the server will register new A and PTR records in BIND that refer to the newly created Docker containers.

Upon receiving a stop or destroy event, the server will remove the associated A and PTR records from named.

Configuration

Bind (named) must be installed on the server's host.

Postgresql must be installed locally to the dnsbridgeserver to be used as a persistent storage of all registered containers. As the server processes, it writes/deletes registered container values from the Postgresql database.

The bridge.sql script must be run to create the dnsbridge database in Postgresql.

The zonefiles distributed with dnsbridge can be used as a model for creating your own DNS zones. The samples include a 3 node setup with a domain name of crunchy.lab as an example.

Note, the named.conf file specifes that no recursion is allowed, you might want to turn this on for your environment.

Testing

Verify your /etc/resolv.conf file has your as your primary DNS the host you have just installed dnsbridge server upon, you should see something similar to:

search crunchy.lab
nameserver 192.168.56.103
nameserver 192.168.0.1

if you notice that your primary DNS server is not in the /etc/resolv.conf after a reboot, it means your PEERDNS setting in your networking is not set to "no", see /etc/sysconfig/network-script/ifcfg files for details.

Verify that dnsbridgeserver and dnsbridgeclient are running:

ps ax | grep dnsbridge

After installation, you can test the install by issuing the following (as root):

/cluster/bin/add-host.sh 192.168.56.103 test.crunchy.lab

This command should register a new host.

You can then use the 'dig' command to make sure it resolves the name:

dig test.crunchy.lab

This should show that the name resolves using ns.crunchy.lab as the DNS nameserver.