Laravel Out of memory error on ubuntu server

I have memory error in Ubuntu hosting(I created it a pair of weeks ago) under Digital Ocean:

root@ubuntu-boxBooking-Dev:/var/www/html/box-booking# lsb_release -d; uname -r; uname -i
Description:    Ubuntu 16.04.4 LTS
4.4.0-130-generic
x86_64

root@ubuntu-boxBooking-Dev:/var/www/html/box-booking# free -m
              total        used        free      shared  buff/cache   available
Mem:            992         325         562          35         104         518
Swap:             0           0           0

I had laravel 5.5 app installed. I pulled changes from git and had to install intervention/image :

# composer require intervention/image 

Using version ^2.4 for intervention/image
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)

mmap() failed: [12] Cannot allocate memory

mmap() failed: [12] Cannot allocate memory
PHP Fatal error:  Out of memory (allocated 586162176) (tried to allocate 20480 bytes) in /usr/share/php/Composer/DependencyResolver/Rule.php on line 66

Fatal error: Out of memory (allocated 586162176) (tried to allocate 20480 bytes) in /usr/share/php/Composer/DependencyResolver/Rule.php on line 66
root@ubuntu-boxBooking-Dev:/var/www/html/box-booking# 
root@ubuntu-boxBooking-Dev:/var/www/html/box-booking# lsb_release -d; uname -r; uname -i

Also I tried:

# composer update
Loading composer repositories with package information
Updating dependencies (including require-dev)
  - Removing doctrine/dbal (v2.6.3)
The following exception is caused by a lack of memory and not having swap configured
Check https://getcomposer.org/doc/articles/troubleshooting.md#proc-open-fork-failed-errors for details

I see not having swap configured error description above and 0 value in free command above. Is it issue and how to fix it?

Also installing Ubuntu hosting under Digital Ocean I did not notice any swap options...

Aslo can be rebooting of the system salve the problem? Usually I reboot the ubuntu(I use kubuntu 18 on my laptop) running under root:

reboot

Is it what I have to run in my case or other command preferable?

Thanks!

via Chebli Mohamed