external-dns: AWS provider doesn't support multiple IPs for ingress

I’m using the nginx ingress controller on bare metal, but the domain I want to update is hosted on Route53. When attempting an update in --once mode, I get the following output:

time="2017-07-11T09:39:31-04:00" level=info msg="config: &{Master: KubeConfig: Sources:[ingress] Namespace: FQDNTemplate: Compatibility: Provider:aws GoogleProject: DomainFilter:[k.oneill.net.] AzureConfigFile:/etc/kubernetes/azure.json AzureResourceGroup: Policy:sync Registry:txt TXTOwnerID:default TXTPrefix: Interval:1m0s Once:true DryRun:false LogFormat:text MetricsAddress::7979 Debug:true}" 
time="2017-07-11T09:39:31-04:00" level=info msg="Connected to cluster at https://k1:6443" 
time="2017-07-11T09:39:31-04:00" level=debug msg="Endpoints generated from ingress: default/plexpy: [plexpy.k.oneill.net -> 172.19.74.134 (type "") plexpy.k.oneill.net -> 172.19.74.135 (type "") plexpy.k.oneill.net -> 172.19.74.147 (type "")]" 
time="2017-07-11T09:39:31-04:00" level=info msg="Changing records: CREATE {
  Action: "CREATE",
  ResourceRecordSet: {
    Name: "plexpy.k.oneill.net",
    ResourceRecords: [{
        Value: "172.19.74.134"
      }],
    TTL: 300,
    Type: "A"
  }
} ..." 
time="2017-07-11T09:39:31-04:00" level=info msg="Changing records: CREATE {
  Action: "CREATE",
  ResourceRecordSet: {
    Name: "plexpy.k.oneill.net",
    ResourceRecords: [{
        Value: "172.19.74.135"
      }],
    TTL: 300,
    Type: "A"
  }
} ..." 
time="2017-07-11T09:39:31-04:00" level=info msg="Changing records: CREATE {
  Action: "CREATE",
  ResourceRecordSet: {
    Name: "plexpy.k.oneill.net",
    ResourceRecords: [{
        Value: "172.19.74.147"
      }],
    TTL: 300,
    Type: "A"
  }
} ..." 
time="2017-07-11T09:39:31-04:00" level=info msg="Changing records: CREATE {
  Action: "CREATE",
  ResourceRecordSet: {
    Name: "plexpy.k.oneill.net",
    ResourceRecords: [{
        Value: "\"heritage=external-dns,external-dns/owner=default\""
      }],
    TTL: 300,
    Type: "TXT"
  }
} ..." 
time="2017-07-11T09:39:31-04:00" level=info msg="Changing records: CREATE {
  Action: "CREATE",
  ResourceRecordSet: {
    Name: "plexpy.k.oneill.net",
    ResourceRecords: [{
        Value: "\"heritage=external-dns,external-dns/owner=default\""
      }],
    TTL: 300,
    Type: "TXT"
  }
} ..." 
time="2017-07-11T09:39:31-04:00" level=info msg="Changing records: CREATE {
  Action: "CREATE",
  ResourceRecordSet: {
    Name: "plexpy.k.oneill.net",
    ResourceRecords: [{
        Value: "\"heritage=external-dns,external-dns/owner=default\""
      }],
    TTL: 300,
    Type: "TXT"
  }
} ..." 
time="2017-07-11T09:39:31-04:00" level=error msg="InvalidChangeBatch: The request contains an invalid set of changes for a resource record set 'A plexpy.k.oneill.net.'
	status code: 400, request id: 5e5c4473-663e-11e7-ab1e-73be49546003" 

I believe this is occurring because the Route53 API doesn’t allow creating multiple A records for a single name, but instead expects you to create a single A record with multiple ResourceRecordSet entries.

I think that the AWS provider needs to be changed to combine these A and probably TXT record entries before submitting the change set. I’d be glad to do this work if that fix seems acceptable. I tend to think that the easiest way to do this is to add a filter func that would coalesce records under the same name and RR type.

I’ve tested this against 0.3 and against master and had the same problem.