Overload Protection in SailFin

SailFin has been designed to provide a certain quality of service in terms of the response times, call rate, etc ..  These QoS parameters might be compromised if there is a sudden increase in the load (Calls per second) directed at SailFin or because of some additional load on the CPU on which SailFin is running.  It is important to protect the system under these conditions so that the users are not affected by these fluctuations.
  SailFin has an Overload protection system that would get triggered if certain system attributes like the memory/CPU utilization increases beyond a certain pre-configured threshold. The "Overload Protection Manager (OLP) " is implemented as a pluggable layer in SailFin, which enables it to be easily inserted and configured. The OLP,  when enabled intercepts every request/response (SIP/Http) that enters SailFin and allows it to be processed only if the system is within the configured threshold values. A 503 response is returned back to the client if the request enters the system which is already overloaded either because of CPU or memory utilization. The OLP layer interception happens as soon as the request is parsed and framed, and this early interception guarantees that it consumes the least possible resources while accomplishing its functionality.
The OLP functionlity is disabled by default in the SailFin server, and can be configured quite easily by following the following steps.

1. Enable OLP by inserting the Overload Protection Manager into the interception stack, this can be done by setting an element property under the sip-container element of the configuration. The property name is "olpInserted" and should be set to "true" as shown below.

asadmin set server-config.sip-container.property.olpInserted=true
server-config.sip-container.property.olpInserted = true
Please note that the server has to be restarted after changing the above property for it to take effect.
2. Configure the OLP to perform memory or CPU (or both) protection shown below

For CPU regulation
asadmin set server-config.sip-container.property.CpuOverloadRegulation=true

or

For Memory regulation
asadmin set server-config.sip-container.property.MemOverloadRegulation=true


After steps 1 and 2 the overload protection is enabled and would use the threshold values from code defaults.

3. You can configure the threshold values too. Following are the threshold properties that can be configured and their default values

IrThreshold :  Default value is 70
Threshold of the cpu for initial requests (range 0-100%). A 503 response will be returned when this level is reached.
E.g asadmin set server-config.sip-container.property.IrThreshold=15

MemIrThreshold :  Default value is 85
Sets the threshold of the memory for initial requests (range 0-100%). A 503 response will be returned when this level is reached
E.g asadmin set server-config.sip-container.property.MemIrThreshold=50


SrThreshold:  Default value is 90
Sets the threshold of the cpu for subsequent requests (range 0-100%).
E.g asadmin set server-config.sip-container.property.SrThreshold=90

HttpThreshold:  Default value is 70
Sets the threshold of the cpu for http requests (range 0-100%)
E.g asadmin set server-config.sip-container.property.HttpThreshold=60

MemHttpThreshold :  Default value is 85
Sets the threshold of the memory for http requests (range 0-100%)
E.g asadmin set server-config.sip-container.property.MemHttpThreshold=80

MmThreshold:  Default value is 99
Sets the threshold of the cpu for max load possible for handling messages (range 0-100%), for both Http and Sip. The message, request/response will be dropped in case of SIP.
asadmin set server-config.sip-container.property.MmThreshold=70

MemMmThreshold: Default value is 99
Sets the threshold of the memory for max load possible for handling messages (range 0-100%) for both Http and Sip. The message, request/response will be dropped in case of SIP.
asadmin set server-config.sip-container.property.MemMmThreshold=50

4. Enhance protection algorithm by modifying the sampling parameters

SampleRate:  Default value is 2
Sets the sample rate of updating the overload protection levels. Must be a positive value.
E.g asadmin set server-config.sip-container.property.SampleRate=5

NumberOfSamples:  Default value is 5
Sets the number of consequence samples that is needed before overload is  raised. The sample rate could minimum be set to 2.
E.g asadmin set server-config.sip-container.property.NumberOfSamples=3

 
Following screenshots  show the configuration and the log file when the system is overloaded


            Fig 1: Domain.xml with Cpu protection at 15%



            Fig 2. Server.log when cpu utilization is more than 15%.



            Fig 3: sipp load generator running invite scenario,

The 900 unexpected messages are the 503 responses received when system is overloaded. Behaviour on a multi-cpu machine may be slightly different because of the way in which the CPU utilization may be calculated.