Migration from 4.1 vcl

[Dridi Boukelmoune]

> > Probably mostly third-party VMODs, since Varnish 6.x still supports
> > the VCL 4.0 syntax.
>
> Any specific info on migration of vmods?
> I mostly use the "bundled" vmods[1], but occasionally others like libvmod-sqlite3[2].
>
> If I wanted to convert or upgrade them, do you have any hints or info on what is likely to break and why?
> Can these vmods still be built in the same way with 6.0?

The problem with third-party VMODs is that we don't control them, so
if some idiot [1] decides to change a VMOD's API then VCL making use
of it will need some amount of rewriting when upgrading. You shouldn't
have a problem with bundled VMODs, otherwise we made a mistake.

When it comes to third-party VMODS an upgrade from Varnish 4.1 to 6.x
needs to be studied on a case-by-case basis. Worst case scenario the
module is not even available for the Varnish version you with to
upgrade to.

Dridi

[1] https://github.com/dridi/libvmod-querystring