Dynamic Process Allocation in Apache Server Xiaobo Zhou Yu Cai Ganesh K. Godavari C. Edward Chow

Introduction Degrading DDoS attacks. We want a web server system which can provide clients with differentiated services of proportional response time Two ways: A) admission control and traffic classification: classify the incoming traffic into different queues with different QoS requirement. B) dynamic resource management (our focus): dynamically control the number of processes assigned to each class.

System Architect

Problem Formulation We use M /M /1 queue to model the web server traffic. Proportional-delay of response time for two classes 1 and 2. Assumption of processing rate:

Problem Formulation We want to achieve the resource allocation by process allocation in Apache. The ratio of process allocation can be calculated by:

Process Allocation Strategies 1. A Fixed Process Allocation Strategy 32 total processes, 3:1 ratio, so assign 24:8 to each port. No control over the number of active processes. 2. An Adaptive Process Allocation Strategy Assure all allocated processes are active If non-active, proportionally decrease the processes If all active, proportionally increase the processes

Dynamic Process Allocation Algorithm

Implementation in Apache We modify Apache to make it listen to two ports (80, 8000). The traffic of class 1 will be routed to port 80, and class 2 to port 8000 by admission control. We dynamically control the number of processes allocated for each port, while maintaining a process ratio specified in a ratio file. It is achieved by modifying the child_main() function in http_main.c file of apache. The Process forking and killing is still handled by Apache itself.

System Implementation

Performance Evaluation Use two HP PC(PIII 1GHz, 516M RAM, Redhat 9, 100M Ethernet connection) as router and task web server. Use four HP PC(PIII 233MHz, 96M RAM, Redhat 9, 100M Ethernet connection) to generate http request. Use Httperf and Webbench as the request generator. They can generate http requests with Poisson distribution. The apache we used is version 1.3.29. In the experiments, the system first warmed up for 100 time units. We collect the response time during the next 1000 time units. We average the result after 50 runs. Then we change the system load and repeat the above process.

Fixed Process Adaptation

Fixed Process Adaptation We set the arrival rate ratio to be 3:1, and want to achieve response time ratio 1:3. We calculate the ratio and assign the max number of processes to each port. Since we have no control over the ratio of active process, the result show it is not possible to achieve proportional response time without dynamic process adaptation.

With Dynamic Process Adaptation

With Dynamic Process Adaptation

With Dynamic Process Adaptation

With Dynamic Process Adaptation With dynamic process adaptation, we have better control over the ratio of active process. Therefore, we can achieve proportional response time at range 30% – 80 % system load. It the load is too light or too heavy, it is hard to control.

Class 1 Fixed and Class 2 Change

Class 1 Fixed and Class 2 Change We set class 1 traffic at 40% system load, and change the class 2 traffic, so the overall system load is from 40 - 90%. We can achieve proportional response time when class 2 traffic is not too light(<15%) or too heavy(>40%).

Class 1 change and Class 2 fixed

Class 1 change and Class 2 fixed We set class 2 traffic at 10% system load, and change the class 1 traffic, so the overall system load is from 10 - 80%. We can achieve proportional response time when the traffic is not too light(<40%).

Future Work Find better dynamic process allocation algorithm dealing with light traffic and heavy traffic. Combine admission control and traffic classification together Add feedback and notification mechanism in the system.