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diff --git a/content/blog/2020-08-22-redirect-github-pages.md b/content/blog/2020-08-22-redirect-github-pages.md new file mode 100644 index 0000000..f92ae07 --- /dev/null +++ b/content/blog/2020-08-22-redirect-github-pages.md @@ -0,0 +1,137 @@ ++++ +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) |