Usually rules don't more around, and if they do it's likely
that rules/alerts with the same name stay in the same order.
If rules/alerts with the same name are added/removed this
could cause a blip for one cycle, but this is unavoidable
without requiring rule and alert names to be unique - which we don't
want to do.
In case the execution of all rules takes longer than the configured rule
evaluation interval, one or more iterations will be skipped. This needs
to be visible to the opterator.
This is based on https://github.com/prometheus/prometheus/pull/1997.
This adds contexts to the relevant Storage methods and already passes
PromQL's new per-query context into the storage's query methods.
The immediate motivation supporting multi-tenancy in Frankenstein, but
this could also be used by Prometheus's normal local storage to support
cancellations and timeouts at some point.
For Weaveworks' Frankenstein, we need to support multitenancy. In
Frankenstein, we initially solved this without modifying the promql
package at all: we constructed a new promql.Engine for every
query and injected a storage implementation into that engine which would
be primed to only collect data for a given user.
This is problematic to upstream, however. Prometheus assumes that there
is only one engine: the query concurrency gate is part of the engine,
and the engine contains one central cancellable context to shut down all
queries. Also, creating a new engine for every query seems like overkill.
Thus, we want to be able to pass per-query contexts into a single engine.
This change gets rid of the promql.Engine's built-in base context and
allows passing in a per-query context instead. Central cancellation of
all queries is still possible by deriving all passed-in contexts from
one central one, but this is now the responsibility of the caller. The
central query context is now created in main() and passed into the
relevant components (web handler / API, rule manager).
In a next step, the per-query context would have to be passed to the
storage implementation, so that the storage can implement multi-tenancy
or other features based on the contextual information.
These tests have been added after the /graph changes and therefore
already test the new syntax.
This commit has to be reverted together with the previous one to get
back to the old new state. *sigh*
So far, out-of-order samples during rule evaluation were not logged,
and neither scrape health samples. The latter are unlikely to cause
any errors. That's why I'm logging them always now. (It's alway highly
irregular should it happen.) For rules, I have used the same plumbing
as for samples, just with a different wording in the message to mark
them as a result of rule evaluation.
The chunk encoding was hardcoded there because it mostly doesn't
matter what encoding is chosen in that test. Since type 1 is
battle-hardened enough, I'm switching to type 2 here so that we can
catch unexpected problems as a byproduct. My expectation is that the
chunk encoding doesn't matter anyway, as said, but then "unexpected
problems" contains the word "unexpected".
This considers static labels in the equality of alerts to
avoid falsely copying state from a different alert definition with
the same name across reloads.
To be safe, it also copies the state map rather than just its pointer
so that remaining collisions disappear after one evaluation interval.
This gives up on the idea to communicate throuh the Append() call (by
either not returning as it is now or returning an error as
suggested/explored elsewhere). Here I have added a Throttled() call,
which has the advantage that it can be called before a whole _batch_
of Append()'s. Scrapes will happen completely or not at all. Same for
rule group evaluations. That's a highly desired behavior (as discussed
elsewhere). The code is even simpler now as the whole ingestion buffer
could be removed.
Logging of throttled mode has been streamlined and will create at most
one message per minute.
It's actually happening in several places (and for flags, we use the
standard Go time.Duration...). This at least reduces all our
home-grown parsing to one place (in model).
When an evaluation group runs initially, it waits a deterministic
amount of time. During that time it also has to accept
a termination singnal so shutdown doesn't hang during the first
evaluation iteration after a configuration reload.
Fixes#1307
Goutham Veeramachaneni