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zk_watcher 0.3.2

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.

Contributing to this code

Code contributions can be made through the Nextdoor Gerrit Code Review system. In order to contribute, you will want to follow these instructions:

Nextdoor Code Review System

Place the following lines into ~/.ssh/config::

Host review.opensource.nextdoor.com
Port 29418
User <YOUR USERNAME>

Then verify that you can connect to Gerrit::

$ ssh review.opensource.nextdoor.com
****    Welcome to Gerrit Code Review    ****

Hi Matt Wise, you have successfully connected over SSH.

Unfortunately, interactive shells are disabled.
To clone a hosted Git repository, use:

git clone ssh://<YOUR USERNAME>@review.opensource.nextdoor.com:29418/REPOSITORY_NAME.git

Connection to review.nextdoortest.com closed.

Install and configure git-change::

$ sudo easy_install pip
$ sudo pip install git-change

Clone the repo and setup your hooks::

$ git clone review.opensource.nextdoor.com:zkwatcher
$ cd zkwatcher
$ etc/configure-repository.sh

Make your change, and submit it::

$ touch MyFile
$ git add MyFile
$ git change create
 
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