DNS caching helps reduce the number of DNS lookups that Oracle Traffic Director needs to perform to resolve client host names to IP addresses. The DNS cache is enabled by default in Oracle Traffic Director and stores IP address-to-DNS name mappings. Each entry in the DNS cache represents a single IP address or DNS name lookup. The DNS cache is used only when DNS lookup is enabled and when Oracle Traffic Director performs operations that require DNS lookup, such as recording client IP addresses and host names in the access log.
For the DNS cache hit rate to be high, the cache should be large enough to store the IP address-to-DNS name mappings for the maximum number of clients that you expect to access Oracle Traffic Director concurrently. You can tune the maximum number of entries allowed in the DNS cache and the cache expiry time. Note that setting the cache size too high might result in wasted memory.
This section contains the following topics:
To view the current DNS cache settings for a configuration, run the get-dns-cache-prop command, as shown in the following example:
tadm> get-dnscache-prop --config=soa
enabled=true
max-entries=1024
max-age=120
You can view the current DNS cache utilization and hit rate in the plain-text perfdump report, as shown in the following example:
DNSCacheInfo: ------------------ enabled yes CacheEntries 0/1024 HitRatio 0/0 ( 0.00%) Async DNS disabled
The first line indicates whether the DNS cache is enabled.
CacheEntries shows the number of entries currently in the DNS cache and the maximum number of entries allowed.
HitRatio is the number of cache hits compared to the number of DNS cache lookups.
The last line indicates whether asynchronous DNS lookup is enabled.
You can configure Oracle Traffic Director to perform DNS lookups by using either its own asynchronous resolver or the operating system's synchronous resolver. DNS lookups performed by using the operating system's resolver are faster.
You configure the DNS cache settings for a configuration by using either the administration console or the CLI.
Configuring DNS Cache Settings Using the Administration Console
To configure DNS cache settings by using the administration console, do the following:
Log in to the administration console, as described in Section 2.3.2, "Accessing the Administration Console."
Click the Configurations button that is situated at the upper left corner of the page.
A list of the available configurations is displayed.
Select the configuration that you want to modify.
In the navigation pane, select Advanced Settings.
The Advanced Settings page is displayed.
Go to the DNS section on the page.
Specify the parameters that you want to change.
On-screen help and prompts are provided for all of the parameters.
When you change the value in a field or tab out of a text field that you changed, the Save button near the upper right corner of the page is enabled.
At any time, you can discard the changes by clicking the Reset button.
After making the required changes, click Save.
A message, confirming that the updated configuration was saved, is displayed in the Console Messages pane.
In addition, the Deployment Pending message is displayed at the top of the main pane. You can either deploy the updated configuration immediately by clicking Deploy Changes, or you can do so later after making further changes as described in Section 4.3, "Deploying a Configuration."
Configuring DNS Cache Settings Using the CLI
To change the DNS cache settings for a configuration, run the set-dns-cache-prop command.
For example, the following command changes the maximum number of entries allowed in the DNS cache to 2048:
tadm> set-dns-cache-prop --config=soa max-entries=2048
OTD-70201 Command 'set-dns-cache-prop' ran successfully.
For the updated configuration to take effect, you should deploy it to the Oracle Traffic Director instances by using the deploy-config command.
For more information about the CLI commands mentioned in this section, see the Oracle Traffic Director Command-Line Reference or run the commands with the --help option.