MySQL connections don't recover after MySQL restart, with single DB host

[peteroyle]

/kind bug

What happened: When using MySQL as the database, with just a single MySQL host (so MYSQL_SNDHOST=''), if the MySQL server is restarted for maintenance, all calls to RestComm will fail until RestComm itself is restarted.

What you expected to happen: RestComm should gracefully recover the disconnected MySQL connections in the pool so that eventually calls can continue without manual intervention.

How to reproduce it (as minimally and precisely as possible): Start up restcomm with a primary MySQL host configured, and MYSQL_SNDHOST=''. Restart MySQL. Make a call to RestComm and observe that the call does not connect, and a stack trace is produced with a message such as "Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost"

Continue trying to make calls and note that the situation never improves until you restart RestComm.

Anything else we need to know?: There is already the necessary configuration to fix this in config-mysql.sh, but it's only ever applied if MYSQL_SNDHOST is a non-empty string. I am about to create a pull request which basically copies the missing configuration to the "datasource" element which is applied when MYSQL_SNDHOST=''.

I'm not sure why there is a difference there, maybe there's a reason for it that I'm missing?

Environment:

• Restcomm Connect version (from startup logs): 8.3.0-92
• Cloud provider or hardware configuration: EC2, m4.large instance
• OS (e.g. from /etc/os-release): CentOS 6
• Kernel (e.g. uname -a): 2.6.32-696.16.1.el6.x86_64 #1 SMP Wed Nov 15 16:51:15 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
• Deployment method (e.g. docker-compose, with linked docker-compose.yml file, or application server info + deployment option): Ansible unzips and configures some of the config files such as advanced.cfg etc
• Others:

[gsaslis]

Thanks a lot @peteroyle for the complete and well-documented issue. <3

@leftyb can you please take a look at this one?