Azure Front Door in front of a static website

In the previous post, I wrote about hosting a simple static website on an Azure Storage Account. To enable a custom URL such as https://blog.baeke.info, you can add Azure CDN. If you use the Verizon Premium tier, you can configure rules such as a http to https redirect rule. This is similar to hosting static sites in an Amazon S3 bucket with Amazon CloudFront although it needs to be said that the http to https redirect is way simpler to configure there.

On Twitter, Karim Vaes reminded me of the Azure Front Door service, which is currently in preview. The tagline of the Azure Front Door service is clear: “scalable and secure entry point for fast delivery of your global applications”.

Azure Front Door Service Preview

The Front Door service is quite advanced and has features like global HTTP load balancing with instant failover, SSL offload, application acceleration and even application firewalling and DDoS protection. The price is lower that the Verizon Premium tier of Azure CDN. Please note that preview pricing is in effect at this moment.

Configuring a Front Door with the portal is very easy with the Front Door Designer. The screenshot below shows the designer for the same website as the previous post but for a different URL:

Front Door Designer

During deployment, you create a name that ends in azurefd.net (here geba.azurefd.net). Afterwards you can add a custom name like deploy.baeke.info in the above example. Similar to the Azure CDN, Front Door will give you a Digicert issued certificate if you enable HTTPS and choose Front Door managed:

Front Door managed SSL certificate

Naturally, the backend pool will refer to the https endpoint of the static website of your Azure Storage Account. I only have one such endpoint, but I could easily add another copy and start load balancing between the two.

In the routing rule, be sure you select the frontend host that matches the custom domain name you set up in the frontend hosts section:

Routing rule

It is still not as easy as in CloudFront to redirect http to https. For my needs, I can allow both http and https to Front Door and redirect in the browser:

if(window.location.href.substr(0,5) !== 'https'){
window.location.href = window.location.href.replace('http', 'https');
}

Not as clean as I would like it but it does the job for now. I can now access https://deploy.baeke.info via Front Door!

Using certmagic to add SSL to webhookd

A while ago, I stumbled upon https://github.com/ncarlier/webhookd. It is a simple webhook server, written in Go, that can execute shell scripts. To use it, simply install it on a Linux box and execute it. By default, the executable looks at the ./scripts folder and maps each shell script to a URL you can call. It is well documented so do take a look at the GitHub page for full details on its configuration.

Out of the box, webhookd supports basic authentication if you supply a .htpasswd file. It does not, however, support SSL. That can be fixed in several ways though. In my case, I wanted one executable that supports SSL with Let’s Encrypt certificates. As it turns out, there is a great solution for that: https://github.com/mholt/certmagic.

To simplify using webhookd together with certmagic, I forked the webhookd repo and added certmagic support. The fork is here: https://github.com/gbaeke/webhookd. To use it, use go get github.com/gbaeke/webhookd and work from there. The fork could be improved by adding extra parameters for e-mail address and DNS name. For now, change the code by following the steps below:

  • In main.go, search for mail@mail.com and replace it with a valid e-mail address; although not required it is a good practice to supply an e-mail address to the folks at Let’s Encrypt
  • In main.go, search for www.example.com and replace it with a valid DNS name
  • The DNS name you use needs to resolve to the IP address of the machine that runs webhookd; it should be a public IP address because the code uses the HTTP challenger
  • The machine that runs webhookd should expose port 80 and port 443
  • If you want to use the Let’s Encrypt staging servers during testing (recommended) change certmagic.LetsEncryptProductionCA to certmagic.LetsEncryptStagingCA

In my case, the machine that runs webhookd is a small Linux machine running on Microsoft Azure. The DNS name is actually a CNAME record that is an alias for the DNS name of the virtual machine (e.g. vmname.westeurope.cloudapp.azure.com). You are now ready to build webhookd with go build. When it’s ready, just execute webhookd. When you run this the first time, certmagic will notice there is no certificate and will start to talk to Let’s Encrypt using the ACME protocol. By default, HTTP verification is used which just means Let’s Encrypt will tell certmagic to host a file over plain HTTP. When Let’s Encrypt can retrieve that file, it concludes you must be the owner of the DNS name used in the certificate. The certificate will be issued and stored on the file system under $home/.local/share/certmagic/acme.

You will get some messages regarding the certificate request process as shown below. When the cached certificate is found and it is valid, you will just get the Serving HTTP->HTTPS message:

image

Note that you will not be able to bind to low ports like 80 and 443 as a non-root user. So either run webhookd as root or use setcap. For instance sudo setcap cap_net_bind_service=+ep /path/to/webhookd. After running the setcap command, you can run webhookd as a non-root user and it will be able to bind to port 80 and 443.

I also have basic authentication enabled for a user called api. To test the configuration, I can use curl like so:

image

Due to the use of the Let’s Encrypt production CA, there is no need to use the –insecure flag with curl. The certificate is fully trusted on my (Windows) machine. If you pulled down the complete repository, the scripts folder contains a shell script called echo.sh. That script is automatically made available as /echo. Everything the script echoes to stdout is used as output of the HTTP call. Simple but effective!

In a follow-up post, we will take a look at using webhookd to deploy Azure resources using a managed identity and the Azure CLI. Stay tuned!