DNS Service Exception Operations Manual: A Guide to Monitoring and Troubleshooting

in the internet service architecture, DNS is the core of the conversion between domain names and Internet Protocol Addresses. Once there is a problem, users cannot access various network services normally, which brings direct losses to the business. For operation and maintenance personnel, mastering the monitoring methods, troubleshooting logic and emergency handling methods of abnormal DNS services is the key ability to ensure business continuity. This paper will start from a practical point of view, and sort out the whole process operation and maintenance plan of abnormal DNS services for operation and maintenance personnel, covering monitoring and early warning, fault location, emergency recovery and long-term optimization.

How to monitor DNS service abnormalities?

early detection of DNS service abnormalities is the first line of defense for operation and maintenance, an effective monitoring system can issue early warnings before failures affect users, and buy time for investigation and recovery.

1, core indicators monitoring

focus on monitoring the DNS service resolution success rate, response time, request volume fluctuations of these three core indicators. Resolution success rate needs to be maintained above 99.99%, once below the threshold may exist DNS service abnormality; response time should be controlled within 100ms, continuous increase may mean that the server load is too high or network congestion; request volume sudden increase or sudden drop, need to be vigilant DDoS attack or service node offline problem.

2, multi-node detection and verification

deploy multi-region and multi-operator detection nodes, and regularly perform resolution tests on the core domain name to avoid the blind spot of single node monitoring. For example, in the domestic north and south regions and the three major operator networks, if the resolution fails in a certain area, it can quickly locate whether it is a local network problem or a global DNS service abnormality. At the same time, monitor the connectivity of recursive DNS and authoritative DNS to ensure that all nodes of the resolution link are normal.

How to quickly troubleshoot DNS service abnormalities?

when receiving DNS service abnormal warning or user feedback, operation and maintenance personnel need to quickly locate the root cause of the fault according to the standardized process to avoid blind troubleshooting and waste of time.

1, layered positioning fault link

hierarchical troubleshooting from the user side to the server level, first verify whether the local DNS cache is abnormal, and then re-resolve the test after clearing the local cache; then check whether the recursive DNS node is normal, and use the dig or nslookup tool to directly request the recursive node; finally troubleshoot the authoritative DNS server to confirm whether the server running status and domain name configuration records are correct. Through hierarchical troubleshooting, the scope of DNS service abnormalities can be quickly reduced and specific links can be located.

2, log analysis to trace the root

retrieve DNS server request logs and error logs to analyze the characteristics of abnormal requests, such as whether there are a large number of duplicate requests for the same IP and whether there are abnormal domain name resolution requests. If there are a large number of records such as "query timeout" and "denial of service" in the log, it can be combined with monitoring indicators to further confirm whether the server resources are exhausted, firewall interception or DNS service abnormalities caused by misconfiguration.

Third, DNS service abnormal emergency recovery how to do?

confirm the root cause of the DNS service abnormality, the emergency recovery operation needs to be performed immediately, and the normal access of the user should be restored first, and then the subsequent root cause repair should be carried out.

1, switch standby service node

If the primary DNS node has hardware failure or serious performance problems, immediately switch to the pre-deployed backup node to ensure that the resolution service is not interrupted. Before switching, verify that the configuration of the backup node is consistent with the primary node to avoid new DNS service abnormalities caused by configuration differences. At the same time, update the DNS server address record at the domain name registrar to ensure that the global resolution link handover is completed.

2, temporarily adjust the cache policy

If there is a configuration error in the authoritative DNS, it cannot be repaired in a short time, and the cache time of the recursive DNS can be temporarily increased, so that the client can use the resolution results in the cache to reduce the impact range of the failure. After the authoritative DNS configuration repair is completed, the normal cache policy will be gradually restored to avoid secondary DNS service abnormalities caused by cache expiration.

4. How to prevent DNS service abnormalities from happening again?

emergency recovery is only a palliative measure and a long-term prevention mechanism can be established to reduce the probability of DNS service abnormalities from the root cause.

1, build highly available architecture

use multi-node cluster to deploy DNS services, the master and standby nodes are synchronized in real time, and combined with Anycast technology implementation intelligent scheduling of traffic, when a node fails, the traffic will automatically switch to the healthy node. In addition, select the deployment nodes of different operators and different regions to avoid the global DNS service abnormality caused by power failure or network failure in a single computer room.

2, regular drills and configuration audit

conduct DNS failure emergency drills every quarter, simulate server downtime, DDoS attacks, configuration errors and other scenarios, and check the response speed and recovery ability of the operation and maintenance team. At the same time, monthly configuration audits are carried out to check the correctness of domain name resolution records, the rationality of TTL settings, and the security of permission configuration. Find potential configuration risks in time to avoid DNS service abnormalities caused by human errors.

To sum up, the operation and maintenance management of abnormal DNS services is a closed-loop system, from monitoring and early warning to find problems in advance, to hierarchical investigation to quickly locate the root cause, to emergency recovery to reduce business impact, and finally to prevent failure recurrence through architecture optimization and regular drills. Operation and maintenance personnel need to be proficient in the operation methods of each link and establish a standardized DevOps flow in order to effectively ensure the stability of DNS services and build a solid foundation for the normal operation of the business.