Configurable Denial-Of-Service prevention library for Express

This module is outdated. Please, use DDDoS instead.

Example

var expresss = require("express");
var ddos = require("ddos-express");

var app = express();

app.use(ddos({
    /*Configuration options*/
}));

Configuration

errorData

Data to be passes to the client on DDoS detection. Default: "Not so fast!".

errorCode

HTTP error code to be set on DDoS detection. Default: 429 (Too Many Requests).

weight

Default request weight. 1 by default.

maxWeight

Default maximum allowed weight per IP. 10 by default.

checkInterval

Interval (in milliseconds) to check connections and decrement weights. Default: 1000 (1 second).

rules

List of rules to apply to each request. Example:

    rules: [
        { /*Allow 4 requests accessing the application API per checkInterval*/
            regexp: "^/api.*",
            flags: "i",
            maxWeight: 4,
            queueSize: 4 /*If request limit is exceeded, new requests are added to the queue*/
        },
        { /*Only allow 1 search request per check interval.*/
            string: "/action/search",
            maxWeight: 1
        },
        { /*Allow up to 16 other requests per check interval.*/
            regexp: ".*",
            maxWeight: 16
        }
]

logFunction

A function used for logging detected DDoS. The following arguments are passes to the function:

• req.ip — user's IP address
• req.path — request path
• user.weight — current weight
• rule.maxWeight — maximum allowed weight
• rule.regexp || rule.string — rule pattern

How this module works

Every request is checked against a chain of rules. Rules with a string path pattern are checked first. They are added to a map for the sake of performance. Then the request is checked against every regexp-based rules.

If request path (req.path) matches the rule's pattern, that rule is applied. Other rules are not checked.

User IP is retrieved from the req.ip property. You have to handle proxies (X-Forwarded-For header and such) yourself.

A weight is assigned to each user. Every time a new request is made, the weight is increased. If the weight becomes larger than maxWeight, the errorData is returned to the user along with the errorCode.

Requests which did not match any rule or have passed the test are forwarded to the next middleware/router.

Every checkInterval milliseconds all users are checked. The weights are decremented by the maxWegight. If user's weight becomes less than or equal to 0, that user is deleted from the map.

Example situation

Say weight is 1, maxWeight is 10 and checkInterval is 1000.

A user makes 35 requests in one second. First 10 request pass the module, the other 25 do not. The weight is 35 for now. Then the user stops sending requests.

After 1 second passes by, the weight is decremented by 10 and becomes 25. The user attempts to make one more request, which does not pass. The weight becomes 26.

Two sceonds later (after two checks) the weight is decreased twice and becomes 6. The user attempts to make a request, which now successfully passes the check. The weight becomes 7.