Add AMI to labels scraped during service discovery. (#7386)

Signed-off-by: Martin Lee <martin@martinlee.org>

discovery/ec2/ec2.go

@@ -38,6 +38,7 @@ import (
 
 const (
 	ec2Label                  = model.MetaLabelPrefix + "ec2_"
+	ec2LabelAMI               = ec2Label + "ami"
 	ec2LabelAZ                = ec2Label + "availability_zone"
 	ec2LabelArch              = ec2Label + "architecture"
 	ec2LabelInstanceID        = ec2Label + "instance_id"
@@ -212,6 +213,7 @@ func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 					labels[ec2LabelPublicDNS] = model.LabelValue(*inst.PublicDnsName)
 				}
 
+				labels[ec2LabelAMI] = model.LabelValue(*inst.ImageId)
 				labels[ec2LabelAZ] = model.LabelValue(*inst.Placement.AvailabilityZone)
 				labels[ec2LabelInstanceState] = model.LabelValue(*inst.State.Name)
 				labels[ec2LabelInstanceType] = model.LabelValue(*inst.InstanceType)

docs/configuration/configuration.md

@@ -426,6 +426,7 @@ the public IP address with relabeling.
 
 The following meta labels are available on targets during [relabeling](#relabel_config):
 
+* `__meta_ec2_ami`: the EC2 Amazon Machine Image
 * `__meta_ec2_architecture`: the architecture of the instance
 * `__meta_ec2_availability_zone`: the availability zone in which the instance is running
 * `__meta_ec2_instance_id`: the EC2 instance ID