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Dynamic watermarking with imgproxy and Apache APISIX

· 2 min read

Last week, I described how to add a dynamic watermark to your images on the JVM. I didn't find any library, so I had to develop the feature, or, more precisely, an embryo of a feature, by myself. Depending on your tech stack, you must search for an existing library or roll up your sleeves. For example, Rust offers such an out-of-the-box library. Worse, this approach might be impossible to implement if you don't have access to the source image.

Another alternative is to use ready-made components, namely imgproxy and Apache APISIX. I already combined them to resize images on-the-fly.

Here's the general sequence flow of the process:

Watermark sequence diagram
Click to Preview

  • When APISIX receives a specific pattern, it calls imgproxy with the relevant parameters
  • imgproxy fetches the original image and the watermark to apply
  • It watermarks the original image and returns the result to APISIX

Let's say the pattern is /watermark/*.

We can define two routes:

- uri: "*" #1
"server:3000": 1
- uri: /watermark/* #2
proxy-rewrite: #3
- /watermark/(.*)
- /dummy_sig/watermark:0.8:nowe:20:20:0.2/plain/http://server:3000/$1 #4
"imgproxy:8080": 1 #5
  1. Catch-all route that forwards to the web server
  2. Watermark images route
  3. Rewrite the URL...
  4. ...with an imgproxy-configured route and...
  5. ...forward to imageproxy

You can find the exact rewritten URL syntax in imgproxy documentation. The watermark itself is configured via a single environment variable. You should buy imgproxy's Pro version if you need different watermarks. As a poor man's alternative, you could also set up different instances, each with its watermark, and configure APISIX to route the request to the desired instance.

In this post, we implemented a watermarking feature with the help of imgproxy. The more I think about it, the more I think they make a match made in Heaven.

The complete source code for this post can be found on GitHub.

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