Merge pull request #52586 from xenolinux/EDNS-limitation

CFE-640: Add the EDNS resource limitation details

Author: jeana-redhat

modules/nw-external-dns-operator-logs.adoc

@@ -15,3 +15,45 @@ You can view External DNS Operator logs by using the `oc logs` command.
 ----
 $ oc logs -n external-dns-operator deployment/external-dns-operator -c external-dns-operator
 ----
+
+== External DNS Operator domain name limitations
+
+External DNS Operator uses the TXT registry, which follows the new format and adds the prefix for the TXT records. This reduces the maximum length of the domain name for the TXT records. A DNS record cannot be present without a corresponding TXT record, so the domain name of the DNS record must follow the same limit as the TXT records. For example, DNS record is `<domain-name-from-source>` and the TXT record is `external-dns-<record-type>-<domain-name-from-source>`. 
+
+The domain name of the DNS records generated by External DNS Operator has the following limitations:
+
+[cols="3a,8a",options="header"]
+|===
+|Record type |Number of characters
+
+|CNAME
+|44
+
+|Wildcard CNAME records on AzureDNS
+|42
+
+|A
+|48
+
+|Wildcard A records on AzureDNS
+|46
+
+|===
+
+If the domain name generated by External DNS exceeds the domain name limitation, the External DNS instance gives the following error:
+
+[source,terminal]
+----
+$ oc -n external-dns-operator logs external-dns-aws-7ddbd9c7f8-2jqjh <1>
+----
+<1> The `external-dns-aws-7ddbd9c7f8-2jqjh` parameter specifies the name of the External DNS pod.
+
+.Example output
+[source,terminal]
+----
+time="2022-09-02T08:53:57Z" level=info msg="Desired change: CREATE external-dns-cname-hello-openshift-aaaaaaaaaa-bbbbbbbbbb-ccccccc.test.example.io TXT [Id: /hostedzone/Z06988883Q0H0RL6UMXXX]"
+time="2022-09-02T08:53:57Z" level=info msg="Desired change: CREATE external-dns-hello-openshift-aaaaaaaaaa-bbbbbbbbbb-ccccccc.test.example.io TXT [Id: /hostedzone/Z06988883Q0H0RL6UMXXX]"
+time="2022-09-02T08:53:57Z" level=info msg="Desired change: CREATE hello-openshift-aaaaaaaaaa-bbbbbbbbbb-ccccccc.test.example.io A [Id: /hostedzone/Z06988883Q0H0RL6UMXXX]"
+time="2022-09-02T08:53:57Z" level=error msg="Failure in zone test.example.io. [Id: /hostedzone/Z06988883Q0H0RL6UMXXX]"
+time="2022-09-02T08:53:57Z" level=error msg="InvalidChangeBatch: [FATAL problem: DomainLabelTooLong (Domain label is too long) encountered with 'external-dns-a-hello-openshift-aaaaaaaaaa-bbbbbbbbbb-ccccccc']\n\tstatus code: 400, request id: e54dfd5a-06c6-47b0-bcb9-a4f7c3a4e0c6"
+----