Resolve ip matches on aliases

- If an alias file looks like {"zookeeper-ip":["10.244.0.3], "zookeeper-dns":["f821a07e-82ad-48a8-ba5a-a8391230cb54.zookeeper.default.zookeeper.bosh"]}
both aliases should be returned if they match.

- at the moment link('mylink').instances[0].address will default to ip
so this makes the feature a bit more usable.

[#175435620](https://www.pivotaltracker.com/story/show/175435620)

Author: Maya Rosecrance

src/bosh-dns/dns/server/aliases/config.go

@@ -128,7 +128,7 @@ func (c Config) Resolutions(maybeAlias string) []string {
 	return nil
 }
 
-func (c Config) DomainResolutions(domain string) []string {
+func (c Config) AliasResolutions(domain string) []string {
    var exactMatchAliases []string
     for alias, domains := range c.aliases {
         for _, aliasDomain := range domains {

src/bosh-dns/dns/server/aliases/config_test.go

@@ -176,13 +176,21 @@ var _ = Describe("Config", func() {
 		})
 	})
 
-	Describe("DomainResolutions", func() {
+	Describe("AliasResolutions", func() {
 		It("resolves a FQDNs to the aliases that match", func() {
 			c := MustNewConfigFromMap(map[string][]string{
 				"something.alias":    {"domain"},
 			})
 
-			Expect(c.DomainResolutions("domain.")).To(Equal([]string{"something.alias."}))
+			Expect(c.AliasResolutions("domain.")).To(Equal([]string{"something.alias."}))
+		})
+
+		It("resolves an ip to aliases that match", func() {
+			c := MustNewConfigFromMap(map[string][]string{
+				"something.alias":    {"1.1.1.1"},
+			})
+
+			Expect(c.AliasResolutions("1.1.1.1")).To(Equal([]string{"something.alias."}))
 		})
 
 		It("does not resolve underscored or wildcard domains", func() {
@@ -192,7 +200,7 @@ var _ = Describe("Config", func() {
 				"_.alias-underscore": {"_.domain"},
 			})
 
-			Expect(c.DomainResolutions("1.domain.")).To(Equal([]string{}))
+			Expect(c.AliasResolutions("1.domain.")).To(BeEmpty())
 		})
 
 	})

src/bosh-dns/dns/server/records/record_set.go

@@ -245,12 +245,15 @@ func (r *RecordSet) GetFQDNs(ip string) []string {
 	defer r.recordsMutex.RUnlock()
 
 	uniqueFqnds := make(map[string]bool)
+	for _, alias := range r.mergedAliasList.AliasResolutions(ip) {
+		uniqueFqnds[alias] = true
+	}
 
 	for _, host := range r.hosts {
 		if host.IP == ip {
 			domain := dns.Fqdn(host.FQDN)
 			uniqueFqnds[domain] = true
-			for _, alias := range r.mergedAliasList.DomainResolutions(domain) {
+			for _, alias := range r.mergedAliasList.AliasResolutions(domain) {
 				uniqueFqnds[alias] = true
 			}
 

src/bosh-dns/dns/server/records/record_set_test.go

@@ -342,6 +342,7 @@ var _ = Describe("RecordSet", func() {
 		BeforeEach(func() {
 			aliasList = mustNewConfigFromMap(map[string][]string{
 				"alias1": {"instance0.my-group.my-network.my-deployment.withadot"},
+				"alias2": {"123.123.123.124"},
 			})
 		})
 
@@ -368,8 +369,8 @@ var _ = Describe("RecordSet", func() {
 			recordSet, err = records.NewRecordSet(fileReader, aliasList, fakeHealthWatcher, uint(5), shutdownChan, fakeLogger, fakeFiltererFactory, fakeAliasQueryEncoder)
 			Expect(err).ToNot(HaveOccurred())
 
-			Expect(recordSet.GetFQDNs("123.123.123.123")).To(Equal([]string{"instance0.my-group.my-network.my-deployment.withadot.", "alias1.", "0.my-group.my-network.my-deployment.withadot."}))
-			Expect(recordSet.GetFQDNs("123.123.123.124")).To(Equal([]string{"instance1.my-group.my-network.my-deployment.nodot.", "1.my-group.my-network.my-deployment.nodot."}))
+			Expect(recordSet.GetFQDNs("123.123.123.123")).To(ConsistOf("alias1.", "instance0.my-group.my-network.my-deployment.withadot.", "0.my-group.my-network.my-deployment.withadot."))
+			Expect(recordSet.GetFQDNs("123.123.123.124")).To(ConsistOf("instance1.my-group.my-network.my-deployment.nodot.", "1.my-group.my-network.my-deployment.nodot.", "alias2."))
 			Expect(recordSet.GetFQDNs("123.123.123.125")).To(Equal([]string{"instance2.my-group.my-network.my-deployment.domain.", "2.my-group.my-network.my-deployment.domain."}))
 			Expect(recordSet.GetFQDNs("127.0.0.1")).To(BeEmpty())
 		})