I had some questions about how we should approach supporting header rewrites in Varnish.
As you know, using VCL we can directly rewrite headers by accessing the request and response objects. The concern is how should the user of Traffic Control specify which headers to rewrite or based on what conditions. Normally with Traffic Server we can use something like the plugin.config parameter to specify the header_rewrite plugin with the path to files containing rewrite directives based on ATS supported syntax. Should we expect the user to also provide ATS syntax? While it's doable, it is not that easy to parse this configuration and maintaining it will be non-trivial. We can also expect from the user to input the directives in a Varnish way using VCL. Since it is just like any VCL we will be basically allowing the user to add their own blocks of code whether it's a header rewrite or just a custom logic. I think that would be easy to maintain and will offer more customization but will require more parameters. What do you think? Abdulrahman On Sat, Oct 7, 2023 at 3:44 PM Eric Friedrich <fri...@alum.rpi.edu> wrote: > Great suggestions Abdulrahman! > > I think in terms of base functionality, that header rewrites are very > frequently used, so this might be a good next step. Lots of times extra > response headers are needed, especially if CORS is required. > > Regex remap is also useful because CDNs frequently are asked to modify the > URL, and Varnish has great support for this with regsub() already. > > After that, paying off some tech debt on the testing might make sense? > Would be very cool if we could find a way to integrate varnishtest somehow > as its purpose built for testing VCL functionality > > Best, > Eric > > On Thu, Oct 5, 2023 at 6:56 AM Abdulrahman Elawady <aelaw...@apache.org> > wrote: > > > Hi Everyone, > > > > Now that Varnish is somewhat in a good state with a lot of the basics > done, > > I wanted to discuss with you the next steps for making Varnish a viable > > option as a cache server for Traffic Control. > > > > There are multiple options for what to do next and what to focus on and I > > am interested in your opinions on that. > > > > Some of these options are: > > > > Varnish configuration: > > - Cache server storage configuration. It might not be identical to ATS > due > > to different cache storage models between Varnish and ATS. > > - ATS plugins like: header rewrite, regex remap. Some of the plugins are > > straightforward and supported directly by Varnish while others will need > > some work. > > - DS improvements (dscp, qstring, go_direct...) and backends health > checks. > > - Error pages to match ATS. > > > > Functional Tests: > > - Some integration tests are needed for Varnish to ensure the > functionality > > of VCL files generated are correct and make it easier for future > > development to be integrated. It is somewhat different than ORT tests > > available as it tests the functionality of the cache server itself rather > > than t3c or some baseline configuration files. > > > > Varnish development: > > - It would be great to make Varnish development easier for newcomers and > > people interested. So, some of the previous points could be simplified > into > > good first issues. > > - Varnish configuration package "varnishcfg" could be improved based on > how > > easy it is to add features to it. If it turned out to be somewhat > difficult > > we can see other options like go template language or maybe document it > > more. Of course I can't be the judge of that since I wrote a lot of it so > > hopefully the good first issues might give more insight to that. > > > > Traffic Monitor: > > - After #7805 DS stats will be reported except bytes in and out because > > Varnish does not report this data. So, it might need a solution outside > > Varnish. It's probably not a priority right now but just worth > mentioning. > > > > These are just some ideas of what to do next, feel free to suggest other > > ideas. I am interested in your opinions on what to prioritise and focus > on. > > > > Regards, > > Abdulrahman > > >
