Feike Steenbergen
a56b346295
For the postgresql helper, hardened the code to get "the" cursor of the postgresql instance. For the statuspage, a small status json is returned. To find out what status a PostgreSQL cluster is in we use the cursor (instead of the provided query() function), as the query function does some retrying etc. For the healthcheck we want to simple provide an answer to a simple query, if we have to reconnect, we are not *that* healthy anyway. Dropped catching exceptions in the do_GET block, as the HTTPServer will do that nicely for us anyway.
Governor: A Template for PostgreSQL HA with etcd
There are many ways to run high availability with PostgreSQL; here we present a template for you to create your own custom fit high availability solution using etcd and python for maximum accessibility.
Compose runs a a Postgresql as a service platform, which is highly-available from creation. This is a coded example from our prior blog post: High Availability for PostgreSQL, Batteries Not Included.
Getting Started
To get started, do the following from different terminals:
> etcd --data-dir=data/etcd
> ./governor.py postgres0.yml
> ./governor.py postgres1.yml
From there, you will see a high-availability cluster start up. Test different settings in the YAML files to see how behavior changes. Kill some of the different components to see how the system behaves.
Add more postgres*.yml files to create an even larger cluster.
We provide a haproxy configuration, which will give your application a single endpoint for connecting to the cluster's leader. To configure, run:
> haproxy -f haproxy.cfg
> sh haproxy_status.sh 127.0.0.1 5432 15432
> sh haproxy_status.sh 127.0.0.1 5433 15433
> psql --host 127.0.0.1 --port 5000 postgres
How Governor works
For a diagram of the high availability decision loop, see the included a PDF: postgres-ha.pdf
Requirements on a Mac
Run the following on a Mac to install requirements:
brew install postgresql etcd haproxy libyaml python
pip install psycopg2 pyyaml
Notice
There are many different ways to do HA with PostgreSQL, see the PostgreSQL documentation for a complete list.
We call this project a "template" because it is far from a one-size fits all, or a plug-and-play replication system. It will have it's own caveats. Use wisely.