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+++
date = 2020-08-22
title = "Redirect GitHub Pages from Subdomain to the Top-Level Domain"
description = ""
draft = false
+++
# Short answer
## Step 1
Add a new file CNAME to your GitHub Pages repository containing only one
line: your top-level domain name. E.g.: `example.com`
## Step 2
\[Optional\] but highly recommended
2.1: Remove all other top-level records (prefixed with @) of type A from
your DNS configuration.
2.2: Remove a CNAME record for the second-level domain www if it is
present.
## Step 3
Add these 5 entries to the very top of your DNS configuration:
``` txt
@ A 185.199.108.153
@ A 185.199.109.153
@ A 185.199.110.153
@ A 185.199.111.153
www CNAME your_github_username.github.io.
```
Replace `your_github_username` with your actual GitHub
username.
## Step 4
Wait for your DNS changes to propagate. DNS changes aren\'t effective
immediately. They can take up to a full day to propagate.
# Long answer
This issue has two sides. One is the DNS configuration itself. Another
one is the way GitHub Pages will forward HTTP requests.
We need to know a few things to understand what GitHub is trying to say
in their documentation.
## DNS Entry Types
There are two types of DNS records which interest us: CNAME and A.
`A` is also known as `Apex` or sometimes as
`root entry`. It forwards requests to a specified fixed IP
address. `CNAME` entry forwards requests to a specified URL
(actual valid plain text URL, not an IP address).
## DNS Load balancing
GitHub has one central URL address which accepts all DNS requests for
GitHub Pages: `http://username.github.io`. That URL is
resolved to different IP addresses based on your geographical location.
Website hosted on GitHub Pages is a simple collection of
`HTML`, `CSS` and `JS` files. GitHub
distributes these files to different servers across the globe. So that
when your browser sends a request from Europe, it receives data from a
server in Europe. The same is valid for the requests from Asia and the
USA.
## What GitHub is trying to say
Since `A` records in DNS must contain IP addresses, and they
must be either `185.199.108.153` or
`185.199.109.153` or `185.199.110.153` or
`185.199.111.153`, there is no way to forward requests to a
server located somewhere in Europe or Asia. Your website hosted at
GitHub Pages will be downloaded from a central GitHub Pages server.
There is a minor risk that if GitHub Pages DNS servers
(`x.x.x.153`) are down for some reason, all custom domains
which use fixed GitHub Pages IP addresses will not be accessible (their
DNS requests will not be resolvable).
That is why GitHub strongly suggests to either use a second-level domain
for your GitHub Pages (e.g. `blog.example.com`) or use a DNS
service provider that supports a record type `ALIAS` that
acts as `A` record but forwards request to a URL address
(e.g. `username.github.io`) instead of a fixed IP address.
## How GitHub Pages treats HTTP requests
After a DNS request for `your_github_username.github.io` is
resolved into an IP address, e.g. `185.199.108.153` your
browser sends an HTTP request to that server with an HTTP header
`Host`. Below are `curl` examples that load the
same website (these examples might not work if you are behind a proxy
server):
```sh
curl --header "Host: your_github_username.github.io" http://185.199.108.153/
curl --header "Host: www.example.com" http://185.199.108.153/
curl --header "Host: example.com" http://185.199.108.153/
```
This way GitHub Pages servers know which user website to serve.
> GitHub Pages server will automatically redirect HTTP requests to the
> top-level domain if your `CNAME` file contains
> `example.com` but `www.example.com` is
> requested.
>
> The same is valid if your `CNAME` file contains
> `www.example.com` but the header `Host` in the
> `HTTP` request contains `example.com`.
## Why can\'t I add a `CNAME` record entry that accepts a top-level request (`@`) to my DNS configuration?
Quote from the GitHub Pages documentation:
> Warning: Do not create a CNAME record for your custom apex domain!
> Doing so may cause issues with other services, such as email, on that
> domain.
## References:
1. [Setting up a custom domain with GitHub
Pages](https://docs.github.com/en/github/working-with-github-pages/configuring-a-custom-domain-for-your-github-pages-site)
2. [My custom domain isn\'t
working](https://docs.github.com/en/github/working-with-github-pages/troubleshooting-custom-domains-and-github-pages)
3. [Cannot access my GitHub Pages website by IP
Address](https://serverfault.com/questions/589370/cannot-access-my-github-pages-website-by-ip-address)
4. [How do I set up GitHub Pages to redirect DNS requests from a
subdomain (e.g. www) to the top-level domain (TLD, Apex
record)?](https://stackoverflow.com/questions/23375422/how-do-i-set-up-github-pages-to-redirect-dns-requests-from-a-subdomain-e-g-www)
|
