DNS servers that have already propagated go down and are repeated

When you're seeing DNS servers that previously showed successful propagation suddenly showing as down or failing on tools like dnschecker.org, this can be concerning but is often part of normal DNS behavior. Here are some explanations and solutions:

1. DNS Propagation Timing: DNS changes can take up to 48 hours to fully propagate worldwide. During this period, some DNS servers may show your domain correctly at one point, then appear to "go down" later. This is often due to caching behaviors and how DNS resolvers refresh their information.

2. TTL Values: The Time-to-Live (TTL) values on your DNS records determine how long DNS resolvers cache information before requesting updates. If you're seeing inconsistent results, it could be related to TTL expiration and renewal cycles. Lower TTL values can help speed up propagation but some resolvers might still cache information for longer periods.

3. Nameserver Mismatches: There could be a mismatch between the nameservers listed in your domain registration and those in your Route 53 hosted zone. This can cause inconsistent DNS resolution across different locations.

4. Multiple Hosted Zones: If you have multiple hosted zones for the same domain, this could cause confusion and inconsistent results.

5. Regional Network Issues: Sometimes what appears as DNS servers "going down" is actually a temporary routing or connectivity issue between specific geographic locations and those DNS servers.

To address these issues:

1. Verify Nameserver Configuration: Ensure the nameservers in your domain registration settings match exactly with those in your Route 53 hosted zone.

2. Check for Multiple Zones: Make sure you don't have duplicate hosted zones that might be causing conflicts.

3. Adjust TTL Values: Consider temporarily lowering TTL values on your DNS records to help speed up propagation.

4. Wait for Full Propagation: Allow the full 48-hour propagation period to complete before becoming concerned.

5. Check Glue Records: Ensure your DNS Glue records properly reflect your NS records.

Remember that Route 53 is designed with redundancy, providing multiple nameservers for each hosted zone. Even if one nameserver appears to be having issues, the others should continue to function, maintaining overall DNS resolution for your domain.
Sources
Route 53 domain dns not propagating | AWS re:Post
Dns Check after domain move shows only half success | AWS re:Post
Suddenly the domain connection fails. | AWS re:Post
Connectivity Issue with ns-1259.awsdns-29.orgon Amazon Route 53 | AWS re:Post