Followup for #3014 (502 status)

[dridi]

Now that #3014 is merged, I have two patches to apply on top:

• Fail fetches with 502 status when relevant
• Show that directors can now specify an error status (test coverage only)

We could go further in core code, see commit messages for more information.

[bsdphk]

Split in two (possibly 3) subjects:

1. Does being more informative, ie: 502 vs. 503) responses require VCL bump to 4.2 ? A: YES.

2. Exactly what should be returned and when.

3. What can custom directors return and how/why.

Dridi to make attempt on first point.

[dridi]

I extracted the director question to its own pull request: #3017.

Before I make progress on this topic here is a summary of my digging:

• 502 (bad gateway): the backend response was empty (zero bytes EOF) or junk
• 503 (service unavailable): we couldn't even resolve or connect to a backend
• 504 (gateway timeout): the backend response headers fetch timed out
• 500 (internal server error): none of the above (eg. out of storage or workspace)

In hindsight, return (fail) should have led to a 500 response from day one, we should consider changing this too as part of vcl 4.2 to get back on the standards track (pun intended).

Custom directors (#3017) can be more specific but to be honest I don't see any other status they would use besides the list above. Besides "cluster" directors akin to vmod-director we can have "backend" directors like VBE, a well-behaved custom backend should err with the correct status.

#3017 was extracted to its own pull request because this is doable since #3014. The question now remains for our VBE backend implementation.

[bsdphk]

Ok, here is my decision, relevant for #3017 as well:

We will not change the current 503 behavior in VCL4.1

We will introduce this new behavior in VCL4.2

We can add a facility like pythons "from future import MAGICWORD" to enable the new behavior in branches which do not support VCL4.2. The exact syntax we use is TBD.

[nigoroll]

see also #3017 : It appears to me that this PR should be dropped in favor of the new error handling agreed at VDD19Q3

[dridi]

FYI, this pull request changes behavior, #3017 merely shows that a new ability was granted to directors as a side effect and adds coverage.

[dridi]

Reopening for a future VCL bump.

[dridi]

I pushed a new set of patches because they were lagging 500 commits behind.

This could in theory be merged before even introducing a VCL bump, it does take it into account but cannot add coverage for the new stuff until the chicken-egg dependency is solved.

[dridi]

Brief discussion with @bsdphk: for the VBE director implementation, we can add a new property to enable non-503 status codes depending on the error, disabled by default. We could toggle the default value in a future VCL bump, but we aren't making such plans until we have something concrete.

backend example {
    .host = "example.org";
    .gateway_errors = true;
}