This commit removes the scrapeConfig entirely from Target.
All identity defining parameters are thus immutable now and the mutex
can be removed..
Target identity is now correctly defined by the labels and the full URL.
This in particular includes URL parameters that are not specified in the
label set.
Fingerprint is also removed from hash to remove an unnecessary tight coupling
to the common/model package.
With this commit the scrape pool deduplicates incoming
targets before scraping them. This way multiple target providers
can produce the same target but it will be scraped only once.
This commit updates a target set's scrape configuration
on reload. This will cause all running scrape loops to be
stopped and started again with new parameters.
This commit changes the scraper interface to accept a timestamp
so the reported timestamp by the caller and the timestamp
attached to samples does not differ.
This commit moves Scraper handling into a separate scrapePool type.
TargetSets only manage TargetProvider lifecycles and sync the
retrieved updates to the scrapePool.
TargetProviders are now expected to send a full initial target set
within 5 seconds. The scrapePools preserve target state across reloads
and only drop targets after the initial set was synced.
We group providers by their scrape configuration. Each provider produces
target groups with an unique identifier.
On stopping a set of target providers we cancel the target providers,
stop scraping the targets and wait for the scrapers to finish.
On configuration reload all provider sets are stopped and new ones
are created. This will make targets disappear briefly on configuration
reload. Potentially scrapes are missed but due to the consistent
scrape intervals implemented recently, the impact is minor.
Double acquisition of the RLock usually doesn't blow up, but if the
write lock is called for between the two RLock's, we are deadlocked.
This deadlock does not exist in release-0.17, BTW.
With recent changes to a Target's internal data representation
updating by fullLabels() assigns the additional default
instance label. This breaks target identity comparison and causes
identical targets from service discovery to be constantly swapped.
So far we were using the InstanceIdentifier to compare equality of targets.
This is not always accurate, for example for the blackbox exporter where the
actual target is in the parameter.
