Load Impact

To reduce the risk of someone using Load Impact for DOS-attacks, Load Impact remembers how many tests have been performed to a certain site, and how many bytes that were transferred, and transactions that were made during each test.

Whenever someone tries to start a new test, Load Impact checks to see how many tests have been executed for that target site in the last day (the last 24 hours), and how many bytes have been transferred. Then those values are compared with the allowances for the type of user that tried to start the new test, and if the user has a high enough privilege level, the test is started. I'll give an example:

1. User A starts a test for www.domain.com

2. An hour later, user B also starts a test for www.domain.com

3. 6 hours later, user C tries to start a third test for www.domain.com. User C is anonymous (not logged in), and anonymous users may not start new tests for a site if that site has already been tested two times or more the last 24 hours. User C is therefore denied starting his test.

4. User C then creates a Load Impact Light account (free account) and logs in. After that, he is able to start his test, as Load Impact Light users may start new tests for a site that has been tested less than 4 times the last 24 hours.

5. User D, who is also a Load Impact Light user, logs in an hour later and starts a fourth test to www.domain.com. He tries to run it a second time, but gets denied as Load Impact has now tested www.domain.com four times within the last 24 hours.

6. User D upgrades his account to a Load Impact Basic (premium) account. He is now able to start up to 6 more tests for www.domain.com as a Load Impact Basic user may start new tests as long as less than 10 tests have been started for the site in the last 24 hours.

Load Impact in this way enforces limits on a) how many tests that are started that loads a single IP address, b) the number of bytes transferred to/from a single IP address used in your test. The actual limits, however, are layered and vary depending on your account type. Anonymous users are trusted the least, so they are the first to get prevented from testing a site that is "popular". Registered users are trusted to behave a little bit more, while premium (paying) users are trusted the most.

A tricky thing about this is that e.g. in the example above www.domain.com might have IP address 1.2.3.4 but the HTML code there might refer to an image located on another site - maybe www2.domain.com with IP address 1.2.3.5. Load Impact remembers every byte transferred to or from both of these IP addresses, and if someone tries to start a test that loads something from 1.2.3.5, that test might be stopped because someone else has run too many tests for www.domain.com (1.2.3.4) already, putting load on 1.2.3.5 in the process.

The actual limits are evolving all the time, and may change without warning as we are fine-tuning them, but these are the current ones:

An anonymous user may start a new test if:
- There have been less than 2 tests run in the last 24 hours, that have loaded objects from any specific IP address in the test
- Less than 0.5 GB of data has been transferred to/from any specific IP address in the test, in the last 24 hours
- There has been less than 10 tests run in the last 30 days, that have loaded objects from any specific IP address in the test
- Less than 5 GB of data has been transferred to/from any specific IP address in the test, in the last 30 days

A Load Impact Light user may start a new test if:
- There have been less than 4 tests run in the last 24 hours, that have loaded objects from any specific IP address in the test
- Less than 1 GB of data has been transferred to/from any specific IP address in the test, in the last 24 hours
- There has been less than 10 tests run in the last 30 days, that have loaded objects from any specific IP address in the test
- Less than 5 GB of data has been transferred to/from any specific IP address in the test, in the last 30 days
- He or she (the user) has started less than 10 tests in total in the last 30 days
- He or she (the user) has transferred less than 5 GB of data in total in the last 30 days

A Load Impact Basic user may start a new test if:
- There have been less than 10 tests run in the last 24 hours, that have loaded objects from any specific IP address in the test
- Less than 10 GB of data has been transferred to/from any specific IP address in the test, in the last 24 hours
- There has been less than 50 tests run in the last 30 days, that have loaded objects from any specific IP address in the test
- Less than 50 GB of data has been transferred to/from any specific IP address in the test, in the last 30 days
- He or she (the user) has started less than 50 tests in total in the last 30 days
- He or she (the user) has transferred less than 50 GB of data in total in the last 30 days

A Load Impact Professional user may start a new test if:
- There have been less than 20 tests run in the last 24 hours, that have loaded objects from any specific IP address in the test
- Less than 50 GB of data has been transferred to/from any specific IP address in the test, in the last 24 hours
- There has been less than 100 tests run in the last 30 days, that have loaded objects from any specific IP address in the test
- Less than 300 GB of data has been transferred to/from any specific IP address in the test, in the last 30 days
- He or she (the user) has started less than 150 tests in total in the last 30 days
- He or she (the user) has transferred less than 300 GB of data in total in the last 30 days

A Load Impact Advanced user may start a new test if:
- There have been less than 30 tests run in the last 24 hours, that have loaded objects from any specific IP address in the test
- Less than 200 GB of data has been transferred to/from any specific IP address in the test, in the last 24 hours
- There has been less than 150 tests run in the last 30 days, that have loaded objects from any specific IP address in the test
- Less than 1000 GB of data has been transferred to/from any specific IP address in the test, in the last 30 days
- He or she (the user) has started less than 250 tests in total in the last 30 days
- He or she (the user) has transferred less than 1000 GB of data in total in the last 30 days

If you have a registered account, you can double your limits by using a loadimpact.txt file - read more about loadimpact.txt
Also, there is an article about different account types that you can read.

Last edited by Ragnar (2010-03-02 13:25:22)