Amazon Linux 2でWordPress構築時に500エラー

# 事象
Amazon Linux 2でWordPress構築時に500エラー

# アプローチ
500エラーの場合はプログラムの問題の可能性が高い。

### エラー内容を確認
エラー内容が出力されない設定になっていたので、
アクセス時に実行されるプログラムに一時的に以下のコードを埋め込み、
エラー内容が表示されるようにする。

```
error_reporting(E_ALL);
ini_set('display_errors',1);
```

再度画面にアクセスすると、

```
Parse error: syntax error, unexpected '.', expecting '&' or variable (T_VARIABLE) in /***/wp-includes/function.php on line 1090
```
と表示された。

該当行を見ると、可変長の引数をもつメソッドの定義だったので、
PHPのバージョンを疑って確認すると、
PHP5.4だった。

```
# php -v
PHP 5.4.16 (cli) (built: Oct 31 2019 18:34:05)
Copyright (c) 1997-2013 The PHP Group
```

「...」を使った可変長の引数はPHP5.6からサポートされるため、
バージョンアップが必要。

### PHPのアップデート

Amazon Linux 2 EC2インスタンスのパッケージ管理ツールamazon-linux-extrasで利用可能なPHPのバージョンを確認

```
# amazon-linux-extras
  0  ansible2                 available    \
        [ =2.4.2  =2.4.6  =2.8  =stable ]
  2  httpd_modules            available    [ =1.0  =stable ]
  3  memcached1.5             available    \
        [ =1.5.1  =1.5.16  =1.5.17 ]
  5  postgresql9.6            available    \
        [ =9.6.6  =9.6.8  =stable ]
  6  postgresql10             available    [ =10  =stable ]
  8  redis4.0                 available    \
        [ =4.0.5  =4.0.10  =stable ]
  9  R3.4                     available    [ =3.4.3  =stable ]
 10  rust1                    available    \
        [ =1.22.1  =1.26.0  =1.26.1  =1.27.2  =1.31.0  =1.38.0
          =stable ]
 11  vim                      available    [ =8.0  =stable ]
 15  php7.2                   available    \
        [ =7.2.0  =7.2.4  =7.2.5  =7.2.8  =7.2.11  =7.2.13  =7.2.14
          =7.2.16  =7.2.17  =7.2.19  =7.2.21  =7.2.22  =7.2.23
          =7.2.24  =7.2.26  =stable ]
 17  lamp-mariadb10.2-php7.2  available    \
        [ =10.2.10_7.2.0  =10.2.10_7.2.4  =10.2.10_7.2.5
          =10.2.10_7.2.8  =10.2.10_7.2.11  =10.2.10_7.2.13
          =10.2.10_7.2.14  =10.2.10_7.2.16  =10.2.10_7.2.17
          =10.2.10_7.2.19  =10.2.10_7.2.22  =10.2.10_7.2.23
          =10.2.10_7.2.24  =stable ]
 18  libreoffice              available    \
        [ =5.0.6.2_15  =5.3.6.1  =stable ]
 19  gimp                     available    [ =2.8.22 ]
 20  docker=latest            enabled      \
        [ =17.12.1  =18.03.1  =18.06.1  =18.09.9  =stable ]
 21  mate-desktop1.x          available    \
        [ =1.19.0  =1.20.0  =stable ]
 22  GraphicsMagick1.3        available    \
        [ =1.3.29  =1.3.32  =1.3.34  =stable ]
 23  tomcat8.5                available    \
        [ =8.5.31  =8.5.32  =8.5.38  =8.5.40  =8.5.42  =8.5.50
          =stable ]
 24  epel                     available    [ =7.11  =stable ]
 25  testing                  available    [ =1.0  =stable ]
 26  ecs                      available    [ =stable ]
 27  corretto8                available    \
        [ =1.8.0_192  =1.8.0_202  =1.8.0_212  =1.8.0_222  =1.8.0_232
          =1.8.0_242  =stable ]
 28  firecracker              available    [ =0.11  =stable ]
 29  golang1.11               available    \
        [ =1.11.3  =1.11.11  =1.11.13  =stable ]
 30  squid4                   available    [ =4  =stable ]
 31  php7.3                   available    \
        [ =7.3.2  =7.3.3  =7.3.4  =7.3.6  =7.3.8  =7.3.9  =7.3.10
          =7.3.11  =7.3.13  =stable ]
 32  lustre2.10               available    \
        [ =2.10.5  =2.10.8  =stable ]
 33  java-openjdk11           available    [ =11  =stable ]
 34  lynis                    available    [ =stable ]
 35  kernel-ng                available    [ =stable ]
 36  BCC                      available    [ =0.x  =stable ]
 37  mono                     available    [ =5.x  =stable ]
 38  nginx1                   available    [ =stable ]
 39  ruby2.6                  available    [ =2.6  =stable ]
 40  mock                     available    [ =stable ]
 41  postgresql11             available    [ =11  =stable ]
 42  php7.4                   available    [ =stable ]
 43  livepatch                available    [ =stable ]
 44  python3.8                available    [ =stable ]
 45  haproxy2                 available    [ =stable ]
 46  collectd                 available    [ =stable ]
 47  aws-nitro-enclaves-cli   available    [ =stable ]
 48  R4                       available    [ =stable ]
 49  kernel-5.4               available    [ =stable ]
 50  selinux-ng               available    [ =stable ]
 51  php8.0                   available    [ =stable ]
```
PHP7.2が可能なのでPHP7.2にアップデートする。

```
# amazon-linux-extras enable php7.2
  0  ansible2                 available    \
        [ =2.4.2  =2.4.6  =2.8  =stable ]
  2  httpd_modules            available    [ =1.0  =stable ]
  3  memcached1.5             available    \
        [ =1.5.1  =1.5.16  =1.5.17 ]
  5  postgresql9.6            available    \
        [ =9.6.6  =9.6.8  =stable ]
  6  postgresql10             available    [ =10  =stable ]
  8  redis4.0                 available    \
        [ =4.0.5  =4.0.10  =stable ]
  9  R3.4                     available    [ =3.4.3  =stable ]
 10  rust1                    available    \
        [ =1.22.1  =1.26.0  =1.26.1  =1.27.2  =1.31.0  =1.38.0
          =stable ]
 11  vim                      available    [ =8.0  =stable ]
 15  php7.2=latest            enabled      \
        [ =7.2.0  =7.2.4  =7.2.5  =7.2.8  =7.2.11  =7.2.13  =7.2.14
          =7.2.16  =7.2.17  =7.2.19  =7.2.21  =7.2.22  =7.2.23
          =7.2.24  =7.2.26  =stable ]
 17  lamp-mariadb10.2-php7.2  available    \
        [ =10.2.10_7.2.0  =10.2.10_7.2.4  =10.2.10_7.2.5
          =10.2.10_7.2.8  =10.2.10_7.2.11  =10.2.10_7.2.13
          =10.2.10_7.2.14  =10.2.10_7.2.16  =10.2.10_7.2.17
          =10.2.10_7.2.19  =10.2.10_7.2.22  =10.2.10_7.2.23
          =10.2.10_7.2.24  =stable ]
 18  libreoffice              available    \
        [ =5.0.6.2_15  =5.3.6.1  =stable ]
 19  gimp                     available    [ =2.8.22 ]
 20  docker=latest            enabled      \
        [ =17.12.1  =18.03.1  =18.06.1  =18.09.9  =stable ]
 21  mate-desktop1.x          available    \
        [ =1.19.0  =1.20.0  =stable ]
 22  GraphicsMagick1.3        available    \
        [ =1.3.29  =1.3.32  =1.3.34  =stable ]
 23  tomcat8.5                available    \
        [ =8.5.31  =8.5.32  =8.5.38  =8.5.40  =8.5.42  =8.5.50
          =stable ]
 24  epel                     available    [ =7.11  =stable ]
 25  testing                  available    [ =1.0  =stable ]
 26  ecs                      available    [ =stable ]
 27  corretto8                available    \
        [ =1.8.0_192  =1.8.0_202  =1.8.0_212  =1.8.0_222  =1.8.0_232
          =1.8.0_242  =stable ]
 28  firecracker              available    [ =0.11  =stable ]
 29  golang1.11               available    \
        [ =1.11.3  =1.11.11  =1.11.13  =stable ]
 30  squid4                   available    [ =4  =stable ]
  _  php7.3                   available    \
        [ =7.3.2  =7.3.3  =7.3.4  =7.3.6  =7.3.8  =7.3.9  =7.3.10
          =7.3.11  =7.3.13  =stable ]
 32  lustre2.10               available    \
        [ =2.10.5  =2.10.8  =stable ]
 33  java-openjdk11           available    [ =11  =stable ]
 34  lynis                    available    [ =stable ]
 35  kernel-ng                available    [ =stable ]
 36  BCC                      available    [ =0.x  =stable ]
 37  mono                     available    [ =5.x  =stable ]
 38  nginx1                   available    [ =stable ]
 39  ruby2.6                  available    [ =2.6  =stable ]
 40  mock                     available    [ =stable ]
 41  postgresql11             available    [ =11  =stable ]
  _  php7.4                   available    [ =stable ]
 43  livepatch                available    [ =stable ]
 44  python3.8                available    [ =stable ]
 45  haproxy2                 available    [ =stable ]
 46  collectd                 available    [ =stable ]
 47  aws-nitro-enclaves-cli   available    [ =stable ]
 48  R4                       available    [ =stable ]
 49  kernel-5.4               available    [ =stable ]
 50  selinux-ng               available    [ =stable ]
  _  php8.0                   available    [ =stable ]
Now you can install:
 # yum clean metadata
 # yum install php-cli php-pdo php-fpm php-json php-mysqlnd
```

上記の文言通り下記のコマンドを実行

```
# yum clean metadata

# yum install php-cli php-do php-fpm php-json php-mysqlnd
```

### Apacheを再起動

```
# systemctl restart http
```

これで解決しました。

# 最後に

バージョンをまず先に確認するといいかもしれません。