zk-watcher 0.3.1

Python-based service registration daemon for Apache ZooKeeper

zk_watcher is a Python script that handles registration with an Apache ZooKeeper service.

The goal of zk_watcher is to monitor a particular service on a host machine and register that machine as a provider of that service at a given path on the ZooKeeper service.

A simple example is having zk_watcher monitor Apache httpd by running service apache2 status at a regular interval and registers with ZooKeeper at a given path (say /services/production/webservers). As long as the command returns a safe exit code (0), zk_watcher will register with ZooKeeper that this server is providing this particular service. If the hostname of the machine is web1.mydomain.com, the registration path would look like this

/services/production/webservers/web1.mydomain.com:80

In the event that the service check fails, the host will be immediately de- registered from that path.

Installation

To install, run

python setup.py install

or

pip install zk_watcher

Service Configs

To configure, edit the ‘/etc/zk/config.cfg’ file. The file consists of sections that each point to a particular service you want to monitor and register with ZooKeeper. An example file is provided, but could look like this

[ssh]
cmd: /etc/init.d/sshd status
refresh: 60
service_port: 22
service_hostname: 123.234.123.123
zookeeper_path: /services/ssh
zookeeper_data: { "foo": "bar", "bah": "humbug" }

[apache]
cmd: /etc/init.d/apache status
refresh: 60
service_port: 22
zookeeper_path: /services/web
zookeeper_data: foo=bar, bah=humbug

Authentication

If you wish to create a Digset authentication token and use that for your client session with Zookeeper, you can add the settings to the config file like this

[auth]
user: username
password: 123456

If you do this, please look at the nd_service_registry docs to understand how the auth token is used, and what permissions are setup by default.

Running it

See the ‘zk_watcher.rst’ file for configuration and run-time options.

Caveats

Right now you must install this package as root, or you must create the /etc/zk directory ahead of time and change its ownership to your installation user name. The setup.py uses a hard-coded path (/etc/zk/config.cfg) for the config file, and will fail if it cannot create the file at that path. This will be fixed in the next version.