Remove instance as a special grouping key label in push client

This is in preparation for the introduction of arbitrary labels in the
grouping key. We no longer need to support `instance` as a special case,
and will instead generate a path that combines the job label with
everything passed in a grouping key hash.

Signed-off-by: Chris Sinjakli <chris@sinjakli.co.uk>

lib/prometheus/client/push.rb

@@ -16,20 +16,18 @@ module Client
     class Push
       DEFAULT_GATEWAY = 'http://localhost:9091'.freeze
       PATH            = '/metrics/job/%s'.freeze
-      INSTANCE_PATH   = '/metrics/job/%s/instance/%s'.freeze
       SUPPORTED_SCHEMES = %w(http https).freeze
 
-      attr_reader :job, :instance, :gateway, :path
+      attr_reader :job, :gateway, :path
 
-      def initialize(job:, instance: nil, gateway: DEFAULT_GATEWAY, **kwargs)
+      def initialize(job:, gateway: DEFAULT_GATEWAY, **kwargs)
         raise ArgumentError, "job cannot be nil" if job.nil?
         raise ArgumentError, "job cannot be empty" if job.empty?
 
         @mutex = Mutex.new
         @job = job
-        @instance = instance
         @gateway = gateway || DEFAULT_GATEWAY
-        @path = build_path(job, instance)
+        @path = build_path(job)
         @uri = parse("#{@gateway}#{@path}")
 
         @http = Net::HTTP.new(@uri.host, @uri.port)
@@ -70,12 +68,8 @@ def parse(url)
         raise ArgumentError, "#{url} is not a valid URL: #{e}"
       end
 
-      def build_path(job, instance)
-        if instance && !instance.empty?
-          format(INSTANCE_PATH, ERB::Util::url_encode(job), ERB::Util::url_encode(instance))
-        else
-          format(PATH, ERB::Util::url_encode(job))
-        end
+      def build_path(job)
+        format(PATH, ERB::Util::url_encode(job))
       end
 
       def request(req_class, registry = nil)

spec/prometheus/client/push_spec.rb

@@ -76,22 +76,10 @@
       expect(push.path).to eql('/metrics/job/test-job')
     end
 
-    it 'uses the default metrics path if an empty instance value is given' do
-      push = Prometheus::Client::Push.new(job: 'bar-job', instance: '')
-
-      expect(push.path).to eql('/metrics/job/bar-job')
-    end
-
-    it 'uses the full metrics path if an instance value is given' do
-      push = Prometheus::Client::Push.new(job: 'bar-job', instance: 'foo')
-
-      expect(push.path).to eql('/metrics/job/bar-job/instance/foo')
-    end
-
     it 'escapes non-URL characters' do
-      push = Prometheus::Client::Push.new(job: 'bar job', instance: 'foo <my instance>')
+      push = Prometheus::Client::Push.new(job: '<bar job>')
 
-      expected = '/metrics/job/bar%20job/instance/foo%20%3Cmy%20instance%3E'
+      expected = '/metrics/job/%3Cbar%20job%3E'
       expect(push.path).to eql(expected)
     end
   end