When u use AWS Lightsail, it is highly possible u will encounter a memory limit problem because lightsail only cares about your CPU usage. If your application is a memory eater and u have chosen a cheap one,  you will end up with instance random panic due to the lack of resources.

However, at this time, it usually means that your cue to upgrade your instance. But the CPU usage is still below 10%, there is no need for a higher pay grade, right? So we can make the memory a little bit bigger by setting the swap memory.

Swap memory

Swap memory is a technique that can borrow a part of a hard drive for extra memory. Of course, it will be slow compared to real memory. However, it just works 😂

Create the swap memory

Let’s use the command free -h to see current memory usage:

total        used        free      shared  buff/cache   available
Mem:          966Mi       344Mi        61Mi        12Mi       560Mi       447Mi
Swap:            0B          0B          0B

For now, it looks quite alright, but I can tell you that even a little burst will make my instance panic because the free memory is not enough for my application to handle the requests.

So let’s create the swap memory.

First, we create a file that uses for swap. The size will be the swap memory size, which is usually the same size as your real memory size. Here, 1G.

sudo fallocate -l 1G /swapfile
sudo chmod 600 /swapfile

Now we have created the swap file and have set the correct permission for the file. Let’s tell the system to use it!

sudo mkswap /swapfile
sudo swapon /swapfile

We first mark the swapfile file as a special swap use file. Then we told the system to use this file as a swap.

sudo free -h

              total        used        free      shared  buff/cache   available
Mem:          966Mi       342Mi        60Mi        12Mi       562Mi       449Mi
Swap:         1.0Gi          0B       1.0Gi

Now u can see the swap space is not zero anymore.

Finally, we tell the system, don’t use the swap except for really no memory. I know the swap is really slow, so use it only if necessary.

sudo sysctl vm.swappiness=10
cat /proc/sys/vm/swappiness

Make sure the swapiness is 10 instead of the default 60. Less swappiness will make the system lesser tend to use the swap.

Make the swap permanent

At last, we have to make this change persist in case the instance restarts.

Edit the file /etc/fstab file, add a new line:

/swapfile swap swap defaults 0 0

Then we change the swappiness, edit file /etc/sysctl.conf , add a new line:

vm.swappiness=10

Wrap up

Now, hopefully ur server will not panic again. However, this only solve the problem that small burst caused memory shortage. If ur code/service starts to eats more memory as ur business grows, migrate to a bigger real memory instance is the best choice.

Ref

How To Add Swap Space on AWS Lightsail Server Instance