Load Generating Tool
This directory contains a standalone tool that analyzes the capacity of a browserid server. The tool is run from the command line, applies load to the target server, and outputs the number of "active users" it is simulating at the moment.
XXX: document the command line invocation and usage of the tool.
The following sections document how the load generation tool functions in detail, including a description of the estimations employed by the tool.
Defining an Active User
In order to understand what kind of load an "active user" imparts on browserid servers, we must know precisely what an average active user is.
For the sake of this discussion, an active user uses 4 sites that use BrowserID and visits them 10 times each day. These activities are split across 2 different devices. Further, the average user has 2 different email addresses that they use equally, and forgets their password about every 4 weeks.
The final bit of assumption is growth rate, what percentage of active users in a unit of time are using browserid for the first time. This is interesting as different types of requests (with different costs) are made during initial user signup. We start by assuming a 20/80 split of new to returning users per month.
The next bit of guesswork required is to explain the behaviors of these sites (RPs) that a user visits. The average RP will set authentication cookies with 6 hour duration, such that a user must re-authenticate using browserid at least every 6 hours.
Defining high-level user activities
Given these parameters we can now derive concretely the number of high level user activities we must support per second to support 1M active. This will manifest as activities per second for each of the following distinct activities:
- new user signup - someone who has never used browserid goes through the in-dialog "sign up" flow.
- password recovery - a user of browserid goes through the "i forgot my password" flow
- email addition - a user of browserid adds a new email address to their existing account
- re-authentication - a user of browserid re-authenticates to browserid (they have an expired session, or are using a new device for the first time)
- authenticated user sign-in - a user of browserid with authentication material already on their device, and an active session to browserid, logs into a site
From activities to HTTP requests
Having defined the activities above, each activity corresponds to some number of network requests. In step three, we'll break each activity down into its constituent network transactions in a holistic manner, including all resources loaded from browserid servers (NOTE: we could account for browser caching here with another factor).
The result of this is a description of each activity in terms of network transactions that can be expressed in code.