Re: [VOTE] New API symbols for Parent Selection

[John Rushford <jr...@apache.org>]

+1 add the new API's

John Rushford
jrushford@apache.org

On Tue, Mar 9, 2021 at 10:08 AM Robert O Butts <ro...@apache.org> wrote:

>
>
> ---------- Forwarded message ---------
> From: Robert O Butts <ro...@apache.org>
> Date: Fri, Feb 26, 2021 at 8:46 AM
> Subject: [VOTE] New API symbols for Parent Selection
> To: <de...@trafficserver.apache.org>
>
>
> I'd like to propose adding the following symbols to the API, to make it
> possible for remap plugins to do next-hop parent selection:
>
> enum TSHostStatus
> enum TSHostStatusReason
> TSReturnCode TSHostnameIsSelf(const char *hostname);
> TSReturnCode TSHostStatusGet(const char *hostname, const size_t
> hostname_len, TSHostStatus *status, unsigned int *reason);
> void TSHostStatusSet(const char *hostname, const size_t hostname_len,
> TSHostStatus status, const unsigned int down_time,  const unsigned int
> reason);
> struct TSResponseAction;
> void TSHttpTxnResponseActionSet(TSHttpTxn txnp, TSResponseAction action);
> void TSHttpTxnResponseActionGet(TSHttpTxn txnp, TSResponseAction *action);
>
> I have a PR to do this, as well as a plugin for ConsistentHash parent
> selection:
>
> https://github.com/apache/trafficserver/pull/7467
>
> All new symbols except the ResponseAction ones expose existing things in
> core which are necessary for parent selection.
>
> The ResponseAction struct is a small C struct with the data necessary to
> do parent selection, essentially everything that's a function in Strategies
> today.
>
> In a nutshell, everything in core (HttpTransact.cc) that was `if
> (strategy) { } else { /* old parent */ }` becomes `if
> (response_action.handled) { } else if (strategy) { } else { /* old parent
> */ }`.
>
> This supersedes my previous proposal. The previous proposal was a small
> core change, but had the downside of not being a real Remap plugin, and not
> having access to Continuations, Hooks, etc. The alternative seemed to be
> large core State Machine changes.
>
> I believe this is the best of both worlds: a small core change, while
> still being a real plugin with access to continuations and hooks.
>
> The advantage is immediately evident: in the plugin, all the
> per-transaction hash data is moved into the plugin and stored in the
> continuation, out of core (ParentResult). Which means less logic in core,
> and ParentResult can be deleted if parent.config and core strategies are
> removed. This was impossible with the previous method of dropping the
> strategy object into core.
>
> Feedback welcome, please vote, thanks!
>
>