I'm currently running an ec2 micro instance and i've been finding that the instance occasionally runs out of memory.
Other than using a larger instance size, what else can be done?
10 Answers
599
votes
A fix for this problem is to add swap (i.e. paging) space to the instance.
Paging works by creating an area on your hard drive and using it for extra memory, this memory is much slower than normal memory however much more of it is available.
To add this extra space to your instance you type:
sudo /bin/dd if=/dev/zero of=/var/swap.1 bs=1M count=1024
sudo /sbin/mkswap /var/swap.1
sudo chmod 600 /var/swap.1
sudo /sbin/swapon /var/swap.1
If you need more than 1024 then change that to something higher.
To enable it by default after reboot, add this line to /etc/fstab:
/var/swap.1 swap swap defaults 0 0
223
votes
Swap should take place on the Instance Storage (ephemeral) disk and not an EBS device. Swapping will cause a lot of IO and will increase cost on EBS. EBS is also slower than the Instance Store and the Instance Store comes free with certain types of EC2 Instances.
It will usually be mounted to /mnt but if not run
sudo mount /dev/xvda2 /mnt
To then create a swap file on this device do the following for a 4GB swapfile
sudo dd if=/dev/zero of=/mnt/swapfile bs=1M count=4096
Make sure no other user can view the swap file
sudo chown root:root /mnt/swapfile
sudo chmod 600 /mnt/swapfile
Make and Flag as swap
sudo mkswap /mnt/swapfile
sudo swapon /mnt/swapfile
Add/Make sure the following are in your /etc/fstab
/dev/xvda2 /mnt auto defaults,nobootwait,comment=cloudconfig 0 2
/mnt/swapfile swap swap defaults 0 0
lastly enable swap
sudo swapon -a
43
votes
43
votes
After applying the steps mentioned by ajtrichards you can check if your amazon free tier instance is using swap using this command
cat /proc/meminfo
result:
ubuntu@ip-172-31-24-245:/$ cat /proc/meminfo
MemTotal: 604340 kB
MemFree: 8524 kB
Buffers: 3380 kB
Cached: 398316 kB
SwapCached: 0 kB
Active: 165476 kB
Inactive: 384556 kB
Active(anon): 141344 kB
Inactive(anon): 7248 kB
Active(file): 24132 kB
Inactive(file): 377308 kB
Unevictable: 0 kB
Mlocked: 0 kB
SwapTotal: 1048572 kB
SwapFree: 1048572 kB
Dirty: 0 kB
Writeback: 0 kB
AnonPages: 148368 kB
Mapped: 14304 kB
Shmem: 256 kB
Slab: 26392 kB
SReclaimable: 18648 kB
SUnreclaim: 7744 kB
KernelStack: 736 kB
PageTables: 5060 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 1350740 kB
Committed_AS: 623908 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 7420 kB
VmallocChunk: 34359728748 kB
HardwareCorrupted: 0 kB
AnonHugePages: 0 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
DirectMap4k: 637952 kB
DirectMap2M: 0 kB
16
votes
If you are on t2 instances (t2.micro, t2.medium, t2.small), there is no ephemeral or instance storage available to you. So you need to just create your swap in EBS which depending on your use case may or maynot be a good idea.
Otherwise follow @David 's answer, and create your swap on the ephemeral storage to avoid paying EBS costs.
More info: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/InstanceStorage.html there is a table that shows how much ephemeral storage you get for each instance type.
9
votes
6
votes
Using David's Instance Storage answer initially worked for me (on a m5d.2xlarge) however, after stopping the EC2 instance and turning it back on, I was unable to ssh in to the instance again.
The instance logs reported: "You are in emergency mode. After logging in, type "journalctl -xb" to view system logs, "systemctl reboot" to reboot, "systemctl default" or "exit" to boot into default mode. Press Enter for maintenance"
I instead followed the AWS instructions in this link and everything worked perfectly, including after turning the instance off and on again.
https://aws.amazon.com/premiumsupport/knowledge-center/ec2-memory-swap-file/
sudo dd if=/dev/zero of=/swapfile bs=1G count=4
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
sudo swapon -s
sudo vi /etc/fstab
/swapfile swap swap defaults 0 0
4
votes
We can add swap space in any server
create a file using dd command
#dd if=/dev/zero of=/swapfile bs=1M count=2048
or
#dd if=/dev/zero of=/swapfile bs=1024M count=2
bs is blocksize and count refers to the size in MB or GB
we can use vice versa
After creation change the permission of file :
#chmod 600 /swapfile
Then makeswap the file :
#mkswap /swapfile
Then enable the swap file with swapon command :
#swapon /swapfile
Check with free command whether swap is enabled or not :
#free -h
#swapon -s
1
votes
Try swapspace http://pqxx.org/development/swapspace/
Most distros have it packaged.
On EC2 you might want to change "swappath" to /mnt or high-iops disk.
-4
votes
You can use the following script to add swap on Amazon Linux.
https://github.com/chetankapoor/swap
Download the script using wget:
wget https://raw.githubusercontent.com/chetankapoor/swap/master/swap.sh -O swap.sh
Then run the script with the following format:
sh swap.sh 2G
For a complete tutorial you can visit:
