Out of memory error installing laravel app on server

Installing my laravel 5.8 app on ubuntu 18( under Digital Ocean ) I got error :

Updating dependencies
: mmap() failed: [12] Cannot allocate memory
: mmap() failed: [12] Cannot allocate memory
: PHP Fatal error:  Out of memory (allocated 533733376) (tried to allocate 4096 bytes) in /usr/share/php/Composer/DependencyResolver/RuleSetGenerator.php on line 126
: Out of memory (allocated 533733376) (tried to allocate 4096 bytes) in /usr/share/php/Composer/DependencyResolver/RuleSetGenerator.php on line 126

I check memory and see:

# free
              total        used        free      shared  buff/cache   available
Mem:        1009156      387908      147884       15716      473364      462800

I try to attach swap file and googling I found decision :

# sudo swapon -a
# sudo fallocate -l 1G /`file
> 

and last command hang forever.

Next I tried :

# sudo mkswap /swapfile
mkswap: cannot open /swapfile: No such file or directory
# sudo swapon /swapfile
swapon: cannot open /swapfile: No such file or directory



# cat /proc/partitions 
major minor  #blocks  name

 252        0   26214400 vda
 252        1   26100719 vda1
 252       14       4096 vda14
 252       15     108544 vda15
# fdisk -l || mount | grep sd
Disk /dev/vda: 25 GiB, 26843545600 bytes, 52428800 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: C1F9A1FE-534C-4DAC-9299-5CC180C29DCE

Device      Start      End  Sectors  Size Type
/dev/vda1  227328 52428766 52201439 24.9G Linux filesystem
/dev/vda14   2048    10239     8192    4M BIOS boot
/dev/vda15  10240   227327   217088  106M Microsoft basic data

Partition table entries are not in disk order.

Why error and how to fix it ?

via Chebli Mohamed