Overview

These blueprints provide an easy way to ensure hostnames resolve wherever needed in an Apache Brooklyn blueprint. This pattern can work in any cloud or in containers, and is extremely configurable and extensible.

To use, nodes simply advertise brooklyn_dns.enabled and will automatically be placed under DNS management, either using /etc/hosts or a dedicated BIND DNS server.

Synchronizing /etc/hosts

One approach is to have Brooklyn update the /etc/hosts on all the servers you are interested in, containing the IPs and hostnames for all the servers you're interested in.

To use this, install the brooklyn-dns-etc-hosts-generator.bom to your catalog, then simply add this to your blueprint:

  - type: brooklyn-dns-etc-hosts-generator

And then add this bit of config to every entity (or ancestor whose children you're interested in):

    brooklyn.config:
      # tells the etc-hosts-generator to manage DNS on this server
      brooklyn_dns.enabled: true

As an example, see brooklyn-dns-etc-hosts-sample.yaml.

Using Your Own DNS Server

A more scalable approach is to specify a DNS server to use on each node and update a DNS server.

To use this, install the brooklyn-dns-bind-and-registration.bom to your catalog. You can then have Apache Brooklyn create a BIND DNS server for you by including the brooklyn-dns-bind-server blueprint. You can have VMs registered with that DNS server by setting brooklyn_dns.enabled: true (as in the /etc/hosts example). And you can tell VMs to use the BIND DNS server by adding brooklyn-dns-registration-hook as a child to the machine entity.

This is illustrated in brooklyn-dns-bind-and-registration-sample.yaml.

When to Use Which?

The former is nice in a lightweight environment as it introduces no additional dependencies, but at a cost of SSHing to each node every time any member changes.

The latter is better in a larger environment and where nodes change frequently, avoiding SSHing to nodes (apart from configuring resolv.conf), but of course it involves standing up an extra BIND server. (Note that you can share a BIND server among multiple applications, and the approach could be extended to work with any DNS services which expose a REST API.)

Future Work

This is all TODO:

• Allow an entity to specify multiple hostnames, configuring round-robin DNS if a hostname is used across multiple IP addresses (simple load balancing)
• Clustered BIND servers (easy, it's just a group, collecting the IP's and inserting them at nodes; slightly trickier to randomize the list at each node and to update the BIND configuration at nodes)
• Configure TTL for BIND
• Policy for BIND servers to add the registration-hook and full hostname sensors automatically