Intermittent MySQL connection on Vagrant VirtualBox when Jenkins runs PHPUnit - mysql

Question

We have a Jenkins CI server that runs our suite of tests on every commit, triggered by a GitHub hook.
We recently moved the suite of tests from running locally on the Jenkins server to running inside a VirtualBox/Vagrant VM. This is to ensure that the test configuration matches the dev environment. This is an Ubuntu 14.04 guest running on Ubuntu 14.04 host.
After moving to the VM model, PHPUnit occasionally fails with no connection to MySQL. The error is Can't connect to MySQL server on '127.0.0.1'.
This error is intermittent, not easily reproducible. That is, if I trigger a new build on Jenkins, it usually succeeds. However, when the new build is triggered by the GitHub hook, it fails more often than manually triggered builds, and sometimes succeeds.
Here's what I tried:
sudo service mysql restart before running phpunit
sleep 5 between the mysql restart and phpunit
Connecting to localhost and 127.0.0.1 -- When I tried connecting to localhost, I received intermittent errors Can't connect to MySQL server on '/var/run/mysqld/mysqld.sock'.
Here's the full output of the failed build:
sudo service mysql restart
* Stopping MySQL (Percona Server) mysqld
...done.
* Starting MySQL (Percona Server) database server mysqld
...done.
* Checking for corrupt, not cleanly closed and upgrade needing tables.
sleep 5
sudo service mysql status
* /usr/bin/mysqladmin Ver 8.42 Distrib 5.6.23-72.1, for debian-linux-gnu on x86_64
Server version 5.6.23-72.1-log
Protocol version 10
Connection Localhost via UNIX socket
UNIX socket /var/run/mysqld/mysqld.sock
Uptime: 6 sec
Threads: 1 Questions: 111 Slow queries: 0 Opens: 761 Flush tables: 1 Open tables: 754 Queries per second avg: 18.500
phpunit
PHPUnit 4.6.2 by Sebastian Bergmann and contributors.
Configuration read from /vagrant/phpunit.xml
...........EEE.E.............E............................EEEEE.
Time: 8.51 seconds, Memory: 135.25Mb
1) ProcessDatasetsTest::test_process_on_census_fraction
PDOException: SQLSTATE[HY000] [2003] Can't connect to MySQL server on '127.0.0.1' (111)

Answer 1

I've had intermittent connectivity issues with Mysql on Vagrant, but not precisely related to PHPUnit. Connections were dropping just out of the blue, until I found out there were many boxes running at the same time in virtualbox for the same app. I killed them all, then ran vagrant global-status --purge and I had perfect connections again.

Answer 2

We saw a similar issue on a different Vagrant VM -- Can't connect to MySQL server -- and it turned out to be a memory issue. The VM was out of RAM. This was fixed by adding or increasing a swapfile on the VM:
sudo fallocate -l 1G /swapfile.img
sudo chmod 0600 /swapfile.img
sudo mkswap /swapfile.img
sudo swapon /swapfile.img