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Tuesday July 05, 2005
Avoiding mysql_connect errors by using SMF
As mentioned earlier I spent some time with a customer last week who is deploying
an apache/mysql/php app on Solaris 10. One of the big reasons that they are interested
in using Solaris 10 is due to the Service Management Framework - smf(5). Availability is
critically important for their system, so the restart cababilities of smf(5) were a major
attraction. For a more in depth look into SMF checkout the
SMF Community over on
OpenSolaris.
Why use SMF in this scenario
The major issue these folks wanted to avoid is the dreaded mysql connection errors that
plague apache/mysql/php applications if your database goes down. I guess that pretty much anyone who
has ever browsed a php based site (which is just about everyone who uses the web) has encountered
it at least once or twice. So in order to make use of smf(5) we created two service manifests,
one for the downloaded mysql I mentioned previously and one for the bundled apache daemon
with a dependency to ensure that libphp5 exists, and that the webserver will be shutdown and
restarted if mysql needs to be restarted for any reason. Lets refer to this development
platform as SAMP.
The Manifests
The two manifests are mysql-server.xml and
apache-mp.xml respectively (a tarball
is provided here).
The respective uri's are svc:/application/samp/mysql and svc:/application/samp/apache-mp, with
the apache-mp service having a dependency on the mysql service. The mysql service is dependant on
hitting the multi-user milestone (svc:/milestone/multi-user), this is more by personal choice
than anything else. Both of the manifests also contain dependencies on files in the installation,
just as a sanity check, with apache-mp expecting to find /usr/apache/libexec/libphp5.so and
mysql expecting to find /usr/local/mysql/support-files/mysql.server.
Background install and cleanup
Firstly ensure that you have mysql installed, and php compiled up as mentioned in my previous
post. Please note that for this example we are using a different version of mysql than the one
that comes bundled with Solaris, and as such we have installed it in /usr/local.
Next up we want to remove the legacy run scripts for Apache that are installed by default, now
a caveat here, there isn't any need to remove the K16apache script from /etc/rc2.d, as SMF will
execute these with an argument of 'stop', so we just need to remove /etc/rc3.d/S50apache (its
just a symlink to /etc/init.d/apache if you want to undo this later).
Install Our Manifests
To install our manifests we make use of the svccfg command, first off we validate our manifests
# svccfg validate ./mysql-server.xml
# svccfg validate ./apache-mp.xml
And next up we import them
# svccfg import ./mysql-server.xml
# svccfg import ./apache-mp.xml
The manifests that we have specifed here have an entry of
<create_default_instance enabled='true' />
So our instances will be created immediately, so lets check out whats running in our samp namespace
with svcs.
# svcs -l *samp*
STATE STIME FMRI
online 19:20:17 svc:/application/samp/mysql:default
online 19:20:18 svc:/application/samp/apache-mp:default
And we can take a look at the dependicies that your apache-mp service has with
# svcs -d svc:/application/samp/apache-mp
STATE STIME FMRI
online 11:04:55 svc:/application/samp/mysql:default
A little bit of testing....
Now if you haven't used smf you are probably wondering why go to all of this trouble, so lets give
a quick example. Lets do a kill -9 on our mysqld and see what happens. Before we do that, lets take
a look at the process ids and contract id's for the relevant services.
# svcs -p -l *samp*
fmri svc:/application/samp/mysql:default
name MySQL 4.1.12 (Experimental, Downloaded from mysql.com)
enabled true
state online
next_state none
state_time Tue Jul 05 11:04:55 2005
logfile /var/svc/log/application-samp-mysql:default.log
restarter svc:/system/svc/restarter:default
contract_id 69
dependency require_all/none file://localhost/usr/local/mysql/support-files/mysql.server (online)
dependency require_all/error svc:/milestone/multi-user:default (online)
process 427 /bin/sh ./bin/mysqld_safe --datadir=/usr/local/mysql/data --pid-file=/usr/local
process 450 /usr/local/mysql-standard-4.1.12-pc-solaris2.10-i386/bin/mysqld --defaults-extr
fmri svc:/application/samp/apache-mp:default
name Bundled Apache with PHP 5 and MySQL
enabled true
state online
next_state none
state_time Tue Jul 05 11:04:56 2005
logfile /var/svc/log/application-samp-apache-mp:default.log
restarter svc:/system/svc/restarter:default
contract_id 81
dependency require_all/none file://localhost/usr/apache/libexec/libphp5.so (online)
dependency require_all/error svc:/application/samp/mysql:default (online)
process 598 /usr/apache/bin/httpd
process 599 /usr/apache/bin/httpd
process 600 /usr/apache/bin/httpd
process 601 /usr/apache/bin/httpd
process 602 /usr/apache/bin/httpd
process 603 /usr/apache/bin/httpd
and in for the kill ........
# pkill mysql
Now lets take a look at the service states again...
# svcs *samp*
STATE STIME FMRI
online 11:45:24 svc:/application/samp/apache-mp:default
online 11:45:45 svc:/application/samp/mysql:default
And its all restarted, quite cute, and handy. Just for confirmation lets look at the pids and contract id's
again.
# svcs -vp *samp*
STATE NSTATE STIME CTID FMRI
online - 11:45:24 86 svc:/application/samp/apache-mp:default
11:45:24 704 httpd
11:45:25 705 httpd
11:45:25 706 httpd
11:45:25 707 httpd
11:45:25 708 httpd
11:45:25 709 httpd
online - 11:45:45 88 svc:/application/samp/mysql:default
11:45:44 731 mysqld_safe
11:45:44 748 mysqld
Developing your own manifests
A little side note here, if your developing manifests yourself and you get an error message like
the following
# svccfg validate ./foo.xml
svccfg: couldn't parse document
take a look at xmllint(1), which in the case above where I nuked the closing tag for create_default_instance,
gives
# xmllint ./foo.xml
./foo.xml:91: parser error : Opening and ending tag mismatch: create_default_instance line 34 and service
</service>
^
./foo.xml:92: parser error : expected '>'
</service_bundle>
^
./foo.xml:93: parser error : Premature end of data in tag service_bundle line 28
which is somewhat more usefull than the rather cryptic "couldn't parse document", but I digress.
(2005-07-05 05:39:38.0)
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