Time-To-Live (TTL) specifies the period for which a DNS record is cached on a local DNS server. By default, this period is the TTL value set on the authoritative DNS server.
How TTL takes effect
When a local DNS server receives a DNS query, it sends the query to an authoritative DNS server, such as Alibaba Cloud DNS, to retrieve the DNS record.
The local DNS server caches the retrieved DNS record for the period specified by the TTL. During this period, if the local DNS server receives another query for the same domain name, it returns the cached DNS record to the user instead of sending a new query to the authoritative DNS server.
When the cache on the local DNS server expires, the cached DNS record is purged. If the local DNS server receives another query for the same domain name, it sends a new query to an authoritative DNS server, such as Alibaba Cloud DNS, to retrieve the latest DNS record.
The cache period of a DNS record on a local DNS server is the TTL value set on the authoritative DNS server by default. However, some carriers may adjust the cache policy of local DNS servers. This may prolong the time required for a DNS record modification to take effect.
Configurable TTL values for different editions
The minimum configurable TTL value varies by Alibaba Cloud DNS edition. To set a smaller TTL value, purchase an Hosted Public Zone (Subscription).
Edition | Free Edition | Personal Edition | Enterprise Ultimate Edition |
Minimum TTL value | 600 seconds (10 minutes) | 600 seconds (10 minutes) | 1 second |
Maximum TTL value | 86400 seconds (24 hours) | 86400 seconds (24 hours) | 86400 seconds (24 hours) |
Scenarios
Increase the TTL to reduce recursive DNS queries and accelerate resolution.
DNS records are only changed occasionally. You can increase the TTL to extend the cache period of DNS records on local DNS servers. When a user accesses your website, their local DNS server returns the cached DNS record without performing a recursive query. This can accelerate domain name resolution.
Decrease the TTL to reduce the downtime when you change the server IP address.
When you change a DNS record to a new IP address, the change takes effect at different times across regions because the cache on some local DNS servers has not yet expired. As a result, some users access the new server while other users still access the previous server.
Configuration overview
Check the current TTL of the domain name. Assume that the TTL is 10 minutes.
Change the TTL to the minimum value allowed. For example, if you use the Ultimate Edition of Alibaba Cloud DNS, you can change the TTL to 1 second. Different editions support different TTL values.
Wait 10 minutes for the cache on local DNS servers worldwide to expire. After the cache with the previous TTL expires, local DNS servers send new queries to the authoritative DNS server to retrieve the latest DNS record with the new TTL. You must wait for the previous 10-minute cache to expire before the new 1-second TTL takes effect.
Change the IP address in the DNS record. Because the TTL was changed to 1 second in the previous step, local DNS servers can be updated with the latest DNS record almost immediately.
After local DNS servers are synchronized with the latest record, increase the TTL value again, for example, to 10 minutes. If you leave the TTL at 1 second, caching on local DNS servers is not effective. Each DNS query requires a recursive query, which slows down domain name resolution.
NoteSome local DNS servers may not follow the TTL rules set by the authoritative DNS server. When you run a network probe test, you may find that the DNS records on local DNS servers in some regions are inconsistent with your settings. If this issue occurs, wait for a while and then run the test again.
Procedure
Click the target domain name to go to the Settings.
In the Actions column for the target DNS record, click Edit.
In the Edit Record panel, select a TTL value and click OK.
FAQs
Why can't I set the TTL to 1 second?
The minimum configurable TTL for your Alibaba Cloud DNS edition may not be 1 second. See Configurable TTL values for different editions.
Why does the change still take a long time to take effect after I set the TTL to 1 second?
The new TTL takes effect only after the cache with the previous TTL expires. If the previous TTL was 10 minutes, you must wait 10 minutes for the cache on all local DNS servers to expire. After the cache expires, the new 1-second TTL takes effect, and subsequent changes to the DNS record are updated within 1 second.