AWS EC2でyumが使えない

こんにちは@yukifreeworld12です。
EC2でyumコマンドを使ったところエラーが出て数日ハマったのでメモとして、そして後世の同じエラーにハマった人の為にも...
#1. エラー文
EC2のインスタンス内でyumを使おうとすると以下のエラー文が表示される

One of the configured repositories failed (不明),
 and yum doesn't have enough cached data to continue. At this point the only
 safe thing yum can do is fail. There are a few ways to work "fix" this:

     1. Contact the upstream for the repository and get them to fix the problem.

     2. Reconfigure the baseurl/etc. for the repository, to point to a working
        upstream. This is most often useful if you are using a newer
        distribution release than is supported by the repository (and the
        packages for the previous distribution release still work).

     3. Run the command with the repository temporarily disabled
            yum --disablerepo=<repoid> ...

     4. Disable the repository permanently, so yum won't use it by default. Yum
        will then just ignore the repository until you permanently enable it
        again or use --enablerepo for temporary usage:

            yum-config-manager --disable <repoid>
        or
            subscription-manager repos --disable=<repoid>

     5. Configure the failing repository to be skipped, if it is unavailable.
        Note that yum will try to contact the repo. when it runs most commands,
        so will have to try and fail each time (and thus. yum will be be much
        slower). If it is a very temporary problem though, this is often a nice
        compromise:

            yum-config-manager --save --setopt=<repoid>.skip_if_unavailable=true

Cannot retrieve metalink for repository: epel/x86_64. Please verify its path and try again

#2. 解決策
セキュリティグループのアウトバウンドのルールに以下の開放が必要なポートを追加する。

80/tcp
443/tcp
53/udp

##参考
yum が使えなくなりました。どのようにすればいいですか？

##最後に
今日も見てくれてホンマありがとな!!
記事がええなと思ったらフォローといいねホンマよろしくな!!
(ジョーブログ風に)