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

2. 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.

3. System Architect

4. 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:

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

6. 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

7. Dynamic Process Allocation Algorithm

8. 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.

9. System Implementation

10. 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
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.

11. Fixed Process Adaptation

12. 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.

13. With Dynamic Process Adaptation

14. With Dynamic Process Adaptation

15. With Dynamic Process Adaptation

16. 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.

17. Class 1 Fixed and Class 2 Change

18. 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 %. We can achieve proportional response time
when class 2 traffic is not too light(<15%) or too heavy(>40%).

19. Class 1 change and Class 2 fixed

20. 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 %. We can achieve proportional response time
when the traffic is not too light(<40%).

21. 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.