Add pg_isready post

_posts/2018-01-23-pg_isready.md

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+---
+layout: post
+title:  "Using pg_isready to optimize test runs"
+slug: pg_isready
+date:   2018-01-23 13:00:00 +0000
+categories: postgresql bash
+---
+
+While working with Docker Compose to set up a containerized RSpec testing environment today, I ran into a problem.
+
+RSpec, running in one container, was intermittently trying to access the PostgreSQL database, located in a second container, before it had finished booting. Naturally, this was causing sporadic connection errors and test failures.
+
+The testing environment was distributed, with many discrete Docker Compose applications running in parallel. And PostgreSQL's launch time varied considerably, sometimes being under a couple of seconds, but occasionally taking ten seconds or more.
+
+This meant that naively setting a timeout (`sleep 5 && bundle exec rspec`...) was an unsatisfactory approach. It would have increased the run time of every test environment, but without completely solving the problem.
+
+While researching the most appropriate solution, I discovered a useful tool. [`pg_isready`](https://www.postgresql.org/docs/9.3/static/app-pg-isready.html) allows a PostgreSQL database's status to be queried quickly and simply from a script or the command line.
+
+Once I'd found it, using it in the RSpec container's entrypoint script was simple:
+
+```bash
+#!/bin/bash
+
+set -e
+echo "Launching Rails $RAILS_ENV environment with target: $@"
+
+until pg_isready -q -d my_database_name
+do
+  echo "Waiting for database to be ready..."
+  sleep 1
+done
+
+bundle exec rake db:reset
+bundle exec rspec $@
+```