Kristian Lyngstøl's Blog

Visualizing VCL

Posted on 2015-11-16

I was preparing to upgrade a customer, and ran across a semi-extensive VCL setup. It quickly became a bit hard to get a decent overview of what was going on.

The actual VCL is fairly simple.

To deal with this, I ended up hacking together a tiny awk/shell script to generate a dot graph of how things were glued together. You can find the script at .

The output is somewhat ugly, but useful.


(Click for full version)

Of note:

  • This is so far Varnish 3.0-ish, mainly because of the error-syntax. (So it'll work for 4.x, just without vcl_error-tracking)
  • Green borders: Found the reference and everything is OK.
  • Black border: The sub was referenced, but not found in any VCL file.
  • Red border: The sub was found, but never referenced (doesn't count for subroutines beginning with vcl_, e.g. vcl_recv, etc)

No idea if it's of interest to anyone but me, but I found it useful.