Simple Load Balancing

Simple Load Balancing (SLB) Pools are used to define a pool of up to five IPv4 A records (Primary Records) or IPv6 AAAA records, an HTTP(S) monitor, and a backup (All Fail) IPv4 / IPv6 address. One resource record will be served based upon the Response Method that is configured.

When using Simple Load Balancing, the defined monitor (probe) sends HTTP(S) GET or POST requests from four locations pointed at the target addresses once every five minutes. Optionally, the request to the target system can include HTTP(S) request data, and/or the HTTP response data can be searched for specific content. If no search string is specified, the probe of the target is considered Successful if any non-error HTTP response from the target is received. The availability of the target system is evaluated upon receipt of each successful or unsuccessful probe result from each location.

Creating an SLB Pool

Select either an A or AAAA record type, and then click the +Add Pool button.
Select Simple Load Balancing (SLB) from the Select Pool Type drop-down menu.
Provide the Host and the Points To fields.
Provide the All Fail Record(the backup record).
Include the HTTP Test URL that will be used to verify the service is available.
Click Save when finished.

Editing an SLB Pool

Records

Once your Simple Load Balancing pool is created, you will see three tabs that comprise the pool. The first tab is the Records tab, that displays the primary records for the pool, and allows you to set the Forced State, as well as enabling Probes or not.

Add Primary Record

Click in the Add Primary Record field, and provide an IP address for the new record.
Select the Forced State from the drop-down menu.
1. Not Forced- Indicates the record could be served if the probe succeeds, or will not be served if the probe fails.
2. Forced Active - Indicates the record should be served even if the probe fails and determines that the record cannot be served.
3. Forced Inactive - Indicates the record should NOT be served even if the probe succeeds and indicates that the record can be served.
Select whether Probing should be enabled or not. If Probing is NOT enabled, the primary record cannot be served unless the forced state is set to Forced Active.
Click the +Add button to add the new record to the list of Primary Records.
Always remember to keep your All Fail Record up to date, as this will be the backup record served if the primary records all fail.
Click Save when you are finished adding records to save this list and your settings.

Information

The information tab provides details about how the records will be served and returned. If you make any changes to this section, make sure to click the Save button afterwards.

Description – You can provide a description for the SLB pool if you wish, but by default, it will display the pool name.
TTL – The Time to Live in seconds for the pool.
Response Method – Select a method which is responsible for selecting records to be served in the return response.
- Round Robin - The order of the records being returned is determined in a "Round Robin" fashion, based upon the priority of the active records.
- Random - The order of the records being returned is random, and ignores the priority of the active records.
- Priority Hunt- The order of the records being returned is fixed, and is based on the priority value of the active records (High to Low). The highest priority record is always returned.
Serving Preference – Determines if records will be selected from the Primary Records or the All Fail Records.
- Auto Select - The default serving method, which will serve either the Primary Records or the All Fail Record depending on the probe results (and the forced state) of the primary records.
- Serve Primary - Indicates that only the Primary Records are served based upon the probe results (and the forced state) of the primary records.
- Serve All Fail - Indicates that only the All Fail Record will be served, thereby ignoring the probe results (and the forced state) of the primary records.

Probe Definition

When using Simple Load Balancing, an HTTP(S) probe is automatically configured for the pool. The All Fail Record's IP address is not probed. This probe can be configured for either GET or POST. The Probe monitors the Target System (each record in the Primary Records pool once every 300 seconds from each of four geographic regions.

Response data can optionally be validated for the presence of specific content from the Search String field on a successful response. If no Search String is specified, the probe is considered as successful if any non-error response (not HTTP 2xx response) from the target is received. The probe will follow an HTTP 3xx Redirect received from the target system. Availability of the target system is evaluated upon receipt of each successful or unsuccessful probe result from each location.

From the Probe Definition tab, you can do the following:

HTTP Test URL – Provide an http(s) URL to run a test probe against to verify it can be queried.
HTTP Method – You can select either GET in an attempt to retrieve data from the test probe, or POST to send data to the URL with the test probe.
- If you select POST, the Transmitted Data field will appear, allowing you to specify the data you wish to send.
Search String – You can provide a specific search string that should be present in a test probe response for the probe to be considered successful.
Region Failure Sensitivity – Allows you to specify the conditions under which UltraDNS will serve the All Fail Record instead of one of the Primary Records.
- High - Probes in two or more regions are reporting failure of the probe target
- Low - Probes in ALL (four) regions are reporting failure of the probe target.

Once you have provided all of the Probe details, click the Test Probe button to test your newly configured probe information to verify the functionality of the probe. UltraDNS will attempt to execute the configured probe towards the probe target system. When the test probe completes, the results will be displayed below the pool name of your Simple Load Balancing pool.