Add metrics for the output of "SHOW SLAVE HOSTS"

[zoonage]

Closes: #267

Adds a new sub system to show data about the output of SHOW SLAVE HOSTS. This command shows currently running slaves from the master, however it can be presented in two seperate formats;

This is from an old version of MySQL

mysql> SHOW SLAVE HOSTS;
+-----------+----------------------------+------+-------------------+-----------+
| Server_id | Host                       | Port | Rpl_recovery_rank | Master_id |
+-----------+----------------------------+------+-------------------+-----------+
| 380239978 | backup_server_1 |    0 |                 0 |         1 | 
|  11882498 | backup_server_2 |    0 |                 0 |         1 | 
+-----------+----------------------------+------+-------------------+-----------+
3 rows in set (0.00 sec)

This is from a new version of MySQL

mysql> SHOW SLAVE HOSTS;
+------------+-----------+------+-----------+--------------------------------------+
| Server_id  | Host      | Port | Master_id | Slave_UUID                           |
+------------+-----------+------+-----------+--------------------------------------+
|  192168010 | iconnect2 | 3306 | 192168011 | 14cb6624-7f93-11e0-b2c0-c80aa9429562 |
| 1921680101 | athena    | 3306 | 192168011 | 07af4990-f41f-11df-a566-7ac56fdaf645 |
+------------+-----------+------+-----------+--------------------------------------+

This PR is designed to work with both. However the old version does not contain a slave UUID field, so it is left as an empty string.

This exposes one new metric called mysql_slave_hosts_info. As described in #267 the output is like;

# HELP mysql_slave_hosts_info Information from SHOW SLAVE HOSTS
# TYPE mysql_slave_hosts_info gauge
mysql_slave_hosts_info{server_id="380239978",host="backup_server_1",port="0",master_id="",slave_uuid=""} 1
mysql_slave_hosts_info{server_id="192168010",host="iconnect2",port="3306",master_id="192168011",slave_uuid="14cb6624-7f93-11e0-b2c0-c80aa9429562"} 1

[zoonage]

CI breaking is due to an extra dependency that is not vendored

[zoonage]

How do I get the DCO sign off? Do I have to sign the initial commit somehow? (presumably by a squash or history rewrite of some kind?)

Also how do I do the vendoring? govendor just complains saying Error: Package "/home/aaron/Programming/mysqld_exporter" not a go package or not in GOPATH.. Has anyone got any familiarity with the tool?

[SuperQ]

All commits must contain the Signed-off-by signature. Normally I do this by runninggit rebase -i origin/master and using the "reword" mode to update the commit. But it looks like you're pushing to your fork master, rather than using a branch-based fork workflow.

[zoonage]

Thanks @SuperQ just need to work out this vendoring issue now

[SuperQ]

We normally put an empty line between Go standard libraries and external libraries.

[SuperQ]

It looks like there are a couple of go fmt problems that need to be fixed.

[SuperQ]

It looks like you've included the vendor package as a git submodule. For this project we're using govendor. You will want to do something like this:

go get -u -v github.com/kardianos/govendor
go get -u -v github.com/satori/go.uuid
govendor add github.com/satori/go.uuid@v1.2.0

[SuperQ]

It looks like you need to delete that submodule stuff first before doing the govendor, as govendor isn't able to write out the vendor files.

[zoonage]

Thanks @SuperQ, those builds are succeeding now!

[SuperQ]

LGTM, Thanks!

[SuperQ]

Oh, sorry, I forgot one more thing. Can you document the new collector in the top level README.md?

[zoonage]

@SuperQ Added to the arguments table

[zoonage]

@SuperQ is this OK to go or are there some additional changes required?

[SuperQ]

Oh, sorry! This looks great.