Starting LAMP On Low Memory VMs
out of memory
apache low memory
php low memory
mysql low memory
If you are using a dedicated server with a few GB of RAM then you will not have this problem. But if you are running cloud computing with small virtual server like vultr.com then you may end up in this problem: the mysql/mariadb server will run out of memory.
My server is running MariaDB 5.5 and this is the log file
The problem occurs on mariadb and the system closed the service, but is not the only service that it might crash.
To fix the problem need totweak all major services from the system, in this case: Apache, MariaDB, PHP.
Step 1 - Apache
The default timeout is 60 (seconds)....and is much than needed. I will turn this down to the 20-30 second range.
Enabling KeepAlive can avoid generating/killing to many apache child threads, but if your users tend to only view a page or two, this makes no difference, because apache only persists the thread for a given connection. If you have high user engagement, you probably want KeepAlive on, but you should tune it down to keep your total apache thread count low.
MaxKeepAliveRequests and KeepAliveTimeout
If you enabled KeepAlive on your low memory server, you should reduce the MaxKeepAliveRequests and KeepAliveTimeout.
When starting up, mysql server it allocates all the RAM it needs. By default, it will use around 400MB of RAM, which isn't much ona database server with 4GB of RAM, but it is quite significant for a small virtual machine.
Prefork Module or Worker Module
This is where we can tell apache only generate a fewer number of processes. The defaults here are high, limiting you to a max of 256 servers.You can play with the MinSpareServers, MaxSpareServers, StartServers and MaxRequestsPerChild. Before adding this setting you need to check if you are running on prefork or worker module. Alternatively you can add the settings for both modules.
The http config file is located here:
To edit the file with vi editor run the command:
[firstname.lastname@example.org ~]# vi /etc/httpd/conf/httpd.conf
Add the following data to the config file.
Timeout 30 KeepAlive On MaxKeepAliveRequests 50 KeepAliveTimeout 10 <IfModule prefork.c> StartServers 3 MinSpareServers 2 MaxSpareServers 5 MaxClients 10 MaxRequestsPerChild 1000 </IfModule> <IfModule worker.c> StartServers 3 MinSpareServers 2 MaxSpareServers 5 MaxClients 10 MaxRequestsPerChild 1000 </IfModule>
To check if you are running on prefork or worker module you can run the following command:
[email@example.com ~]# httpd -V
The output for this command will look like this:
[firstname.lastname@example.org ~]# httpd -V Server version: Apache/2.4.6 (CentOS) Server built: Nov 19 2015 21:43:13 Server's Module Magic Number: 20120211:24 Servers loaded: APR 1.4.8, APR-UTIL 1.5.2 Compiled using: APR 1.4.8, APR-UTIL 1.5.2 Architecture: 64-bit Server MPM: <b>prefork</b> threaded: no forked: yes (variable process count) Server compiled with.... -D APR_HAS_SENDFILE -D APR_HAS_MMAP -D APR_HAVE_IPV6 (IPv4-mapped addresses enabled) -D APR_USE_SYSVSEM_SERIALIZE -D APR_USE_PTHREAD_SERIALIZE -D SINGLE_LISTEN_UNSERIALIZED_ACCEPT -D APR_HAS_OTHER_CHILD -D AP_HAVE_RELIABLE_PIPED_LOGS -D DYNAMIC_MODULE_LIMIT=256 -D HTTPD_ROOT="/etc/httpd" -D SUEXEC_BIN="usr/sbin/suexec" -D DEFAULT_PIDLOG="/run/httpd/" -D DEFAULT_SCOREBOARD="logs/apache_runtime_status" -D DEFAULT_ERRORLOG="logs/error_log" -D AP_TYPE_CONFIG_FILE="conf/mime.types" -D SERVER_CONFIG_FILE="conf/httpd.conf"
Dont't forget to restart apache after the config change. From CentOS the command line would be:
[email@example.com ~]# systemctl restart httpd.service
Step 2 - MySQL/MariaDB
We can disable Performance Schema by putting this under the [mysqld] section configuration from my.cnf file.
The my.cnf config file is located here:
Other setting that can be done if you are using InnoDB as engine is to decrease the buffer pool size. To do that put under the [mysqld] section the following line:
performance_schema = off
Don't forget to restart apache after the config change. From CentOS the command line would be:
innodb_buffer_pool_size = 2M
[firstname.lastname@example.org ~]# systemctl restart mariadb.service
Step 3 - PHP
For PHP you can reduce the memory limit. to do that edit
/etc/php.ini and add the following line:
memory_limit = 128M
Don't forget to restart apache httpd after the config change.
The values used in this tutorial are not necessary the best. You can tweak and see what values works better for your server. To see the differences between memory usage before and after you can use the
free -M command.