Add additional labels to custom metrics as well. (#657)

Also, update tests to verify that additional labels are being attached.

Ref: #654
PiperOrigin-RevId: 393196944

Fix a goroutine leaking bug in external probe. (#584)

Fix a bug where our process-wait goroutine will not exit until the probe start context is explicitly canceled. This bug was introduced when we added handling for clean exit (June 2020: CR 318986425).

Also, add a test that would have caught this bug.

PiperOrigin-RevId: 366547916

Add surfacers examples.

Ignore CLOUDPROBER_PORT if set by Kubernetes.

Kubernetes automatically sets the <SERVICE>_PORT environment variable to service URL -  "tcp://<service-ip>:<service-port>". This conflicts with cloudprober's port environment variable CLOUDPROBER_PORT if someone runs cloudprober with service name cloudprober. To solve this, we used to parse CLOUDPROBER_PORT if it started with "tcp://". But this doesn't really work well, if someone wants to expose some other port from cloudprober, e.g. RDS. To avoid this confusion, we should just ignore CLOUDPROBER_PORT if it has been set by Kubernetes.

Context: #476
PiperOrigin-RevId: 333552093

Set HTTP request's host header from target's "fqdn" label if available.

This is to fix:
#438

PiperOrigin-RevId: 325289043

Make target based additional labels easier to identify.

= Enclose target based labels within '@@', for example: @target.label.zone@.
= Add support for adding a label based on target's name, using the keyword @target.name@.

While here also standardize on how we export label through sysvars -- use "label_<labelname>" instead of "labels_<labelname>.

PiperOrigin-RevId: 324673535

Remove DOCKER_IMAGE environment override.

Kubernetes documentation fixes and a new section on kubernetes targets

Fix comments and a typo.

PiperOrigin-RevId: 276327600

Ping probe: Update results map even for the targets that don't resolve.

Earlier we were skipping updating any target specific data structure if target fails to resolve. We should update the results map regardless of wether target resolves or not.

See #264 for more details.

PiperOrigin-RevId: 259473838