基本ベースこちらを参考に進めました。
初心者向け：AWS(EC2)にRailsのWebアプリをデプロイする方法 ②
https://qiita.com/iwaseasahi/items/4666f9a777ba3cf61a05

sshでec2に入り込んでからの作業になります。

~
[~]$ sudo yum update #サーバーのアップデート
[~]$ sudo yum install -y nginx 失敗（amazon linux2だからだと思われる。）（※１）
[~]$ amazon-linux-extras | grep nginx #利用可能なnginxを探す。
nginx1
[~]$ sudo amazon-linux-extras install nginx1  #インストール

[~]$ sudo systemctl start nginx.service   #起動

[~]$ sudo systemctl enable nginx.service　　#ngincの自動起動設定

[~]$ systemctl is-enabled nginx.service　#自動起動の反映のされているか確認
enable                               #enableと出ればオーケー


[~]$ sudo yum install git make gcc-c++ patch openssl-devel libyaml-devel libffi-devel libicu-devel libxml2 libxslt libxml2-devel libxslt-devel zlib-devel readline-devel ImageMagick ImageMagick-devel epel-release

[~]$ sudo yum install http://dev.mysql.com/get/mysql-community-release-el6-5.noarch.rpm


[~]$ sudo yum install nodejs npm --enablerepo=epel  #node.jsのインストールで失敗（※2）
読み込んだプラグイン:extras_suggestions, langpacks, priorities, update-motd
Error getting repository data for epel, repository not found   　　　　　　　

[~]$ curl --silent --location https://rpm.nodesource.com/setup_10.x | sudo bash -
[~]$ sudo yum -y install nodejs

// 確認　バージョンが表示されればOKです~
[~]$ npm -v
[~]$ node -v

rbenvをインストールします。~
[~]$ git clone https://github.com/sstephenson/rbenv.git ~/.rbenv
[~]$ echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bash_profile
[~]$ echo 'eval "$(rbenv init -)"' >> ~/.bash_profile
[~]$ source ~/.bash_profile

ruby-buildをインストールします。~
[~]$ git clone https://github.com/sstephenson/ruby-build.git ~/.rbenv/plugins/ruby-build
[~]$ rbenv rehash

ここでは、バージョン2.5.0をインストールします。~
[~]$ rbenv install -v 2.5.0
[~]$ rbenv global 2.5.0
[~]$ rbenv rehash
[~]$ ruby -v
ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-linux]

[~]$ vi ~/.gitconfig
<.gitconfig中身↓↓↓>
---------------------------------
[user]
  name = Githubのユーザー名
  email = Githubに登録しているメールアドレス

[color]
  ui = true

[url "github:"]
  InsteadOf = https://github.com/
  InsteadOf = git@github.com:
------------------------------------
escキー→:wqで保存してviエディタから抜ける

www配下にRailsを格納するフォルダを作成します。
[~]$ cd /
[~]$ cd /var/www/
[~]$ sudo mkdir projects

[~]$ cd
[~]$ chmod 700 .ssh
[~]$ cd .ssh
[.ssh]$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/ec2-user/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/ec2-user/.ssh/id_rsa.
Your public key has been saved in /home/ec2-user/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:ui7bIxjMd7eUn+ahy9CB5LDVI57KBx24vIxWCWDxoZc ec2-user@ip-10-0-10-225.ap-northeast-1.compute.internal
The key's randomart image is:
+---[RSA 2048]----+
|.o..             |
|..o o. .         |
| ..Eo = o        |
|  .o @ = .       |
| o  B * S.       |
|  +=.+.o+.       |
|  o+=.+o.o..     |
| .. oo.+..+.     |
|    .=+.++.      |
+----[SHA256]-----+
[ec2-user .ssh]$ ls
authorized_keys  id_rsa  id_rsa.pub
[.ssh]$ vi config
[.ssh]$ cat id_rsa.pub
[.ssh]$ chmod 600 config
[.ssh]$ ssh -T github  #失敗
The authenticity of host 'github.com (52.192.72.89)' can't be established.
RSA key fingerprint is SHA256:nThbg6kXUpJWGl7E1IGOCspRomTxdCARLviKw6E5SY8.
RSA key fingerprint is MD5:16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'github.com,52.192.72.89' (RSA) to the list of known hosts.
no such identity: /home/ec2-user/.ssh/aws_git_rsa: No such file or directory
Permission denied (publickey).
[ec2-user@ip-10-0-10-225 .ssh]$ ssh -T git@github.com
Hi (account名)! You've successfully authenticated, but GitHub does not provide shell access.

RSDインスタンスにセキュリティグループを設定後の作業
エンドポイントをあらかじめコピーしておく。（RDS→データベース→対象インスタンス選択すると見つかる）
ここでエンドポイントを使用します。
$ mysql -h エンドポイント -P 3306 -u root -p
例
$ mysql -h christchurches-map-mysql.cbev6lgaewnk.ap-northeast-1.rds.amazonaws.com -P 3306 -u root -p
パスワードを入力します。
Enter password:
RDSにアクセスできました。（※出来ない場合タイポ、パス間違え（※3）、アクセス権限間違えが原因かも）
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 75
Server version: 5.6.27-log MySQL Community Server (GPL)

Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>
データベースを確認します。
mysql> show databases;
+-------------------------------+
| Database                      |
+-------------------------------+
| information_schema            |
| christchurches_map_production |
| innodb                        |
| mysql                         |
| performance_schema            |
| sys                           |
+-------------------------------+
6 rows in set (0.00 sec)
退出します。
$ exit;


[ec2-user@ip-10-0-10-225 ~]$ cd /
[ec2-user@ip-10-0-10-225 /]$ mkdir var
[ec2-user@ip-10-0-10-225 /]$ sudo chown ec2-user var
[ec2-user@ip-10-0-10-225 /]$ cd var
[ec2-user@ip-10-0-10-225 var]$ mkdir www
[ec2-user@ip-10-0-10-225 var]$ sudo chown ec2-user www
[ec2-user@ip-10-0-10-225 var]$ cd www
[ec2-user@ip-10-0-10-225 www]$ mkdir projects
[ec2-user@ip-10-0-10-225 www]$ sudo chown ec2-user projects
[ec2-user@ip-10-0-10-225 www]$ git clone git@github.com:KoyoIshikawa/memos.git
[ec2-user@ip-10-0-10-225 projects]$ git clone git@github.com:KoyoIshikawa/memos.git
Cloning into 'memos'...
remote: Enumerating objects: 183, done.
remote: Counting objects: 100% (183/183), done.
remote: Compressing objects: 100% (137/137), done.
remote: Total 183 (delta 56), reused 151 (delta 30), pack-reused 0
Receiving objects: 100% (183/183), 32.63 KiB | 4.66 MiB/s, done.
Resolving deltas: 100% (56/56), done.



[ec2-user@ip-10-0-10-225 memos]$ gem install bundler
Successfully installed bundler-2.1.2
Parsing documentation for bundler-2.1.2
Done installing documentation for bundler after 3 seconds
1 gem installed
[ec2-user@ip-10-0-10-225 memos]$ bundler -v
Traceback (most recent call last):
	2: from /home/ec2-user/.rbenv/versions/2.5.0/bin/bundler:23:in `<main>'
	1: from /home/ec2-user/.rbenv/versions/2.5.0/lib/ruby/2.5.0/rubygems.rb:308:in `activate_bin_path'
/home/ec2-user/.rbenv/versions/2.5.0/lib/ruby/2.5.0/rubygems.rb:289:in `find_spec_for_exe': can't find gem bundler (>= 0.a) with executable bundler (Gem::GemNotFoundException)
[ec2-user@ip-10-0-10-225 memos]$ vim Gemfile.lock

<Gemfile.lockの中身>
--------------------------------------------------------------------------------------------
BUNDLED WITH
   2.1.2   ※cloneしたアプリとec2のbundlerのversionを合わせる。
--------------------------------------------------------------------------------------------
[ec2-user@ip-10-0-10-225 memos]$ bundle exec rake secret
a3883c3f5042ba9683db5090839416ac7291e1e67f165cc7dbc8312999eda68d0f5fed1f13fce63563398540a3b9456beeb8d6dcb35b38dacc8877ab86f997dd

シークレットを表示します。
$ bundle exec rake secret
数字が表示
設定ファイルに記載します。
$ vi config/secrets.yml
production:
  secret_key_base: ここにsecretを貼り付ける

（※１）Amazon Linux2にnginxをinstallするメモ
https://qiita.com/takayuki_tk/items/aa8e1898743458cebd45
（※２）EC2にRDSの為のmysqlコマンドのみをインストールする
https://joppot.info/2017/04/28/3877
（※３）Amazon RDS DB インスタンスのマスターユーザーパスワードをリセットするにはどうすればよいですか?
https://aws.amazon.com/jp/premiumsupport/knowledge-center/reset-master-user-password-rds/
（※４）[エラーメッセージ] can't find gem bundler (>= 0.a) with executable bundler (Gem::GemNotFoundException)
https://qiita.com/MotohiroSiobara/items/c0d343a160cffc2902ef