EC2にlaravelをデプロイしようとしたらcomposerで詰まりました（初心者目線）

#前提バージョン
laravel 5.8
php 7.2
composer 1.9.3
#エラー箇所
composer installで詰まりました。
足りていないphp関連をインストールしろとアナウンスが出ています。

$ composer install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Warning: The lock file is not up to date with the latest changes in composer.json. You may be getting outdated dependencies. It is recommended that you run `composer update` or `composer update <package name>`.
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - laravel/framework v5.8.35 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.
    - laravel/framework v5.8.35 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.
    - Installation request for laravel/framework v5.8.35 -> satisfiable by laravel/framework[v5.8.35].

#解決方法
$yum install php72-php-mysqlnd php72-php-mbstring php72-php-gd
これでもう一度composer install

$ composer install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Warning: The lock file is not up to date with the latest changes in composer.json. You may be getting outdated dependencies. It is recommended that you run `composer update` or `composer update <package name>`.
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - tijsverkoyen/css-to-inline-styles 2.2.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.
    - tijsverkoyen/css-to-inline-styles 2.2.2 requires ext-dom * -> the requested PHP extension dom is missing from your system.
    - Installation request for tijsverkoyen/css-to-inline-styles 2.2.2 -> satisfiable by tijsverkoyen/css-to-inline-styles[2.2.2].

エラー内容が代わりました。

$sudo yum install php72-php-dom
これで解決

###インストールされたか確認

$ php --iniで実際にインストールされかた確認してみるとたしかにdomが入っていますね。

$ php --ini
Configuration File (php.ini) Path: /etc/opt/remi/php72
Loaded Configuration File:         /etc/opt/remi/php72/php.ini
Scan for additional .ini files in: /etc/opt/remi/php72/php.d
Additional .ini files parsed:      /etc/opt/remi/php72/php.d/20-bz2.ini,
/etc/opt/remi/php72/php.d/20-calendar.ini,
/etc/opt/remi/php72/php.d/20-ctype.ini,
/etc/opt/remi/php72/php.d/20-curl.ini,
/etc/opt/remi/php72/php.d/20-dom.ini,
/etc/opt/remi/php72/php.d/20-exif.ini,
/etc/opt/remi/php72/php.d/20-fileinfo.ini,
/etc/opt/remi/php72/php.d/20-ftp.ini,
/etc/opt/remi/php72/php.d/20-gd.ini,
/etc/opt/remi/php72/php.d/20-gettext.ini,
/etc/opt/remi/php72/php.d/20-iconv.ini,
/etc/opt/remi/php72/php.d/20-json.ini,
/etc/opt/remi/php72/php.d/20-mbstring.ini,
/etc/opt/remi/php72/php.d/20-mysqlnd.ini,
/etc/opt/remi/php72/php.d/20-pdo.ini,
/etc/opt/remi/php72/php.d/20-phar.ini,
/etc/opt/remi/php72/php.d/20-simplexml.ini,
/etc/opt/remi/php72/php.d/20-sockets.ini,
/etc/opt/remi/php72/php.d/20-sqlite3.ini,
/etc/opt/remi/php72/php.d/20-tokenizer.ini,
/etc/opt/remi/php72/php.d/20-xml.ini,
/etc/opt/remi/php72/php.d/20-xmlwriter.ini,
/etc/opt/remi/php72/php.d/20-xsl.ini,
/etc/opt/remi/php72/php.d/30-mysqli.ini,
/etc/opt/remi/php72/php.d/30-pdo_mysql.ini,
/etc/opt/remi/php72/php.d/30-pdo_sqlite.ini,
/etc/opt/remi/php72/php.d/30-wddx.ini,
/etc/opt/remi/php72/php.d/30-xmlreader.ini

ここまで来たらもう一度composer install実行します。
するとcomposer updateしてとアナウンスされました。

$ composer install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Warning: The lock file is not up to date with the latest changes in composer.json. You may be getting outdated dependencies. It is recommended that you run `composer update` or `composer update <package name>`.
Nothing to install or update
Generating optimized autoload files
Warning: Ambiguous class resolution, "App\Http\Requests\ProfileRequest" was found in both "/var/www/html/tree2/tree2/myblog/app/Http/Controllers/IdRequest.php" and "/var/www/html/tree2/tree2/myblog/app/Http/Requests/ProfileRequest.php", the first will be used.
Warning: Ambiguous class resolution, "App\User" was found in both "/var/www/html/tree2/tree2/myblog/app/Http/Controllers/User.php" and "/var/www/html/tree2/tree2/myblog/app/User.php", the first will be 
～（省略）～

composer update実行

[ec2-user@ip-172-31-36-97 myblog]$ composer update
Loading composer repositories with package information
Updating dependencies (including require-dev)
Package operations: 1 install, 39 updates, 0 removals
  - Updating symfony/polyfill-ctype (v1.13.1 => v1.14.0): The following exception is caused by a lack of memory or swap, or not having swap configured
Check https://getcomposer.org/doc/articles/troubleshooting.md#proc-open-fork-failed-errors for details

PHP Warning:  proc_open(): fork failed - Cannot allocate memory in phar:///usr/local/bin/composer/vendor/symfony/console/Application.php on line 952

Warning: proc_open(): fork failed - Cannot allocate memory in phar:///usr/local/bin/composer/vendor/symfony/console/Application.php on line 952

  [ErrorException]
  proc_open(): fork failed - Cannot allocate memory

～（省略）～

なにやらエラーが出ています。
メモリが足りないみたいなので容量を大きくします。

$ sudo /bin/dd if=/dev/zero of=/var/swap.1 bs=1M count=1024
$ sudo /sbin/mkswap /var/swap.1
$ sudo /sbin/swapon /var/swap.1

これでcomposer update→composer installが行けるはず！