Improve negative TTL caching tests.

To better clarify usage and add a second test to ensure the negative TTL
setting is actually being used, rather than the timing just happening to
work for the default TTL (which we saw in a separate branch working on
this with Trafficserver's DNS).

test/proxy/dns/test_negative_caching.rb

@@ -26,33 +26,71 @@ def after_all
     override_config_reset("--router")
   end
 
-  def test_failed_host_down_after_ttl_expires
+  def test_caches_failed_lookups_before_retrying
+    assert_negative_ttl(NEGATIVE_TTL)
+  end
+
+  def test_negative_ttl_can_be_configured
+    negative_ttl = 3
+
+    # Ensure this negative TTL is different enough than the default that we can
+    # distinguish the results in tests.
+    assert_operator(negative_ttl, :<=, (NEGATIVE_TTL - TTL_BUFFER_POS).floor)
+
+    override_config({
+      "dns_resolver" => {
+        "nameservers" => ["[127.0.0.1]:#{$config["unbound"]["port"]}"],
+        "max_stale" => 0,
+        "negative_ttl" => negative_ttl,
+      },
+    }, "--router") do
+      assert_negative_ttl(negative_ttl)
+    end
+  end
+
+  private
+
+  def assert_negative_ttl(negative_ttl)
     prepend_api_backends([
       {
         :frontend_host => "127.0.0.1",
-        :backend_host => "negative-caching-invalid-hostname-begins-resolving.ooga",
-        :servers => [{ :host => "negative-caching-invalid-hostname-begins-resolving.ooga", :port => 9444 }],
-        :url_matches => [{ :frontend_prefix => "/#{unique_test_id}/negative-caching-invalid-hostname-begins-resolving/", :backend_prefix => "/info/" }],
+        :backend_host => unique_test_hostname,
+        :servers => [{ :host => unique_test_hostname, :port => 9444 }],
+        :url_matches => [{ :frontend_prefix => "/#{unique_test_id}/", :backend_prefix => "/info/" }],
       },
     ]) do
-      # The negative TTL caching really begins as soon as the initial
-      # configuration is put into place by runServer (since that's when the
-      # hostname is first seen and the unresolvable status is cached). So start
-      # our timer here.
+      # Make an initial request, which we expect to not succeed, since the
+      # hostname is bad.
+      wait_for_response("/#{unique_test_id}/", {
+        :code => 502,
+      })
+
+      # The negative TTL caching begins after TrafficServer sees the first
+      # request and tries to resolve it. So start our timer after the first
+      # request.
       start_time = Time.now.utc
 
-      wait_for_response("/#{unique_test_id}/negative-caching-invalid-hostname-begins-resolving/", {
+      # Add the DNS record for the previously invalid domain.
+      set_dns_records(["#{unique_test_hostname} 60 A 127.0.0.1"])
+
+      # Ensure that negative caching is in place and the hostname is still not
+      # resolving (despite the DNS being installed now).
+      wait_for_response("/#{unique_test_id}/", {
         :code => 502,
       })
 
-      set_dns_records(["negative-caching-invalid-hostname-begins-resolving.ooga 60 A 127.0.0.1"])
-      wait_for_response("/#{unique_test_id}/negative-caching-invalid-hostname-begins-resolving/", {
+      # Wait for the successful response to resolve once the negative TTL has
+      # expired.
+      wait_for_response("/#{unique_test_id}/", {
         :code => 200,
         :local_interface_ip => "127.0.0.1",
       })
+
+      # Sanity check the results to ensure the results fit within the expected
+      # negative TTL values.
       duration = Time.now.utc - start_time
-      min_duration = NEGATIVE_TTL - TTL_BUFFER_NEG
-      max_duration = NEGATIVE_TTL + TTL_BUFFER_POS
+      min_duration = negative_ttl - TTL_BUFFER_NEG
+      max_duration = negative_ttl + TTL_BUFFER_POS
       assert_operator(min_duration, :>, 0)
       assert_operator(duration, :>=, min_duration)
       assert_operator(duration, :<, max_duration)

test/support/api_umbrella_test_helpers/setup.rb

@@ -279,6 +279,30 @@ def unique_test_id
       @unique_test_id ||= self.location.gsub(/[^\w]+/, "-")
     end
 
+    def unique_test_hostname
+      unless @unique_test_hostname
+        # Replace all non alpha-numeric chars (namely underscores that might be
+        # in the ID) with dashes (since underscores aren't valid for
+        # hostnames).
+        hostname = unique_test_id.downcase.gsub(/[^a-z0-9]+/, "-")
+
+        # Truncate the hostname so the label will fit in unbound's 63 char
+        # limit.
+        hostname = hostname[-56..-1] || hostname
+
+        # Strip first char if it happens to be a dash.
+        hostname.gsub!(/^-/, "")
+
+        # Since we've truncated the test ID, it's possible it's no longer
+        # unique, so append some random chars (but still, fitting within the 63
+        # char limit).
+        hostname = "#{hostname}-#{SecureRandom.hex(3)}"
+
+        @unique_test_hostname = "#{hostname}.test"
+      end
+      @unique_test_hostname
+    end
+
     def next_unique_ip_addr
       @@incrementing_unique_ip_addr = @@incrementing_unique_ip_addr.succ
       @@incrementing_unique_ip_addr.to_s