tunning Ubuntu 12.04 on AWS micro instance

An AWS micro instance has 590M of RAM. Hosting some sites with Apache and Mysql on this instance requires some adjustments to avoid consuming all memory and crashing the server.

Adding a swap file

Default installation of Ubuntu 12.04 server on AWS microinstance comes without swap.

Here are the steps to a add a swap file of 1500Mb or 1.5Gb:

sudo fallocate -l 1500m  /mnt/1500M.swap
sudo chmod 600 /mnt/1500M.swap
sudo mkswap /mnt/1500M.swap

...Setting up swapspace version 1, size = 1535996 KiB
...no label, UUID=bef3f3ec-d1a4-4ec5-857e-19c9ab5c1042

sudo swapon  /mnt/1500M.swap

To verfiy the swap was installed:

cat /proc/swaps

To make the swap change permanent (persist on the next reboot), add the following line to the file /etc/fstab

/mnt/1500M.swap  none  swap  sw  0 0

This is how my /etc/fstab file looks like:

LABEL=cloudimg-rootfs   /    ext4   defaults    0 0

/mnt/1500M.swap  none  swap  sw  0 0

Reducing mysql memory consumption on AWS micro instance

The mysql default install on ubuntu 12.04 can consume more than 400M RAM when the server starts to get some load/traffic. That is too much for a micro instance.

You can try changing the following values in /etc/mysql/my.cnf

# key_buffer original value was 16M
key_buffer             = 8M
# query_cache_size original value was 16M
query_cache_size       = 4M
max_connections        = 40

that should be enough. Here are other values you can try to adjust:

# query cache limit original value was  1M
query_cache_limit       = 512K

## original value was 192K
thread_stack            = 128K

Tunning Apache2 MaxClients

If you get a sudden spike of www requests, there is a chance that apache2 with a default configuration will consume a lot of memory.

edit the file /etc/apache2/apache2.conf find the mpm_prefork_module and reduce MaxClients value:

StartServers          5
MinSpareServers       5
MaxSpareServers      10
##MaxClients          150
## configuration for server with little memory
MaxClients          30
MaxRequestsPerChild   0

Note that this is for apache mpm_prefok, if you installed apache mpm_worked, adjust the MaxClients line in the corresponding section.

Restart the services and monitor

Finally, restart both services and check with a tool like htop:

sudo service mysql restart
sudo service apache2 restart

htop

With htop you should be able to see allocated swap, and memory consumption of every process.