Package org.apache.catalina.filters

Class RateLimitFilter

java.lang.Object

org.apache.catalina.filters.FilterBase

org.apache.catalina.filters.RateLimitFilter

All Implemented Interfaces:

Filter

public class RateLimitFilter
extends FilterBase

Servlet filter that can help mitigate Denial of Service (DoS) and Brute Force attacks by limiting the number of a requests that are allowed from a single IP address within a time window (also referred to as a time bucket), e.g. 300 Requests per 60 seconds.

The filter works by incrementing a counter in a time bucket for each IP address, and if the counter exceeds the allowed limit then further requests from that IP are dropped with a "429 Too many requests" response until the bucket time ends and a new bucket starts.

The RateLimiter implementation can be set via the className init param. The default implementation, org.apache.catalina.util.FastRateLimiter, is optimized for efficiency and low overhead so it converts some configured values to more efficient values. For example, a configuration of a 60 seconds time bucket is converted to 65.536 seconds. That allows for very fast bucket calculation using bit shift arithmetic. In order to remain true to the user intent, the configured number of requests is then multiplied by the same ratio, so a configuration of 100 Requests per 60 seconds, has the real values of 109 Requests per 65 seconds. You can specify a different class as long as it implements the org.apache.catalina.util.RateLimiter interface.

It is common to set up different restrictions for different URIs. For example, a login page or authentication script is typically expected to get far less requests than the rest of the application, so you can add a filter definition that would allow only 5 requests per 15 seconds and map those URIs to it.

You can set enforce to false to disable the termination of requests that exceed the allowed limit. Then your application code can inspect the Request Attribute org.apache.catalina.filters.RateLimitFilter.Count and decide how to handle the request based on other information that it has, e.g. allow more requests to certain users based on roles, etc.

WARNING: if Tomcat is behind a reverse proxy then you must make sure that the Rate Limit Filter sees the client IP address, so if for example you are using the Remote IP Filter, then the filter mapping for the Rate Limit Filter must come after the mapping of the Remote IP Filter to ensure that each request has its IP address resolved before the Rate Limit Filter is applied. Failure to do so will count requests from different IPs in the same bucket and will result in a self inflicted DoS attack.

Field Summary

Fields

Modifier and Type	Field	Description
static final int	DEFAULT_BUCKET_DURATION	default duration in seconds
static final int	DEFAULT_BUCKET_REQUESTS	default number of requests per duration
static final boolean	DEFAULT_ENFORCE	default value for enforce
static final int	DEFAULT_STATUS_CODE	default status code to return if requests per duration exceeded
static final String	DEFAULT_STATUS_MESSAGE	default status message to return if requests per duration exceeded
static final String	RATE_LIMIT_ATTRIBUTE_COUNT	request attribute that will contain the number of requests per duration

Constructor Summary

Constructors

Constructor	Description
RateLimitFilter()

Method Summary

Modifier and Type	Method	Description
void	destroy()	Called by the web container to indicate to a filter that it is being taken out of service.
void	doFilter(ServletRequest request, ServletResponse response, FilterChain chain)	The doFilter method of the Filter is called by the container each time a request/response pair is passed through the chain due to a client request for a resource at the end of the chain.
protected Log	getLogger()
void	init(FilterConfig filterConfig)	Iterates over the configuration parameters and either logs a warning, or throws an exception for any parameter that does not have a matching setter in this filter.
protected boolean	isConfigProblemFatal()	Determines if an exception when calling a setter or an unknown configuration attribute triggers the failure of the this filter which in turn will prevent the web application from starting.
void	setBucketDuration(int bucketDuration)
void	setBucketRequests(int bucketRequests)
void	setEnforce(boolean enforce)
void	setRateLimitClassName(String rateLimitClassName)
void	setStatusCode(int statusCode)
void	setStatusMessage(String statusMessage)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

DEFAULT_BUCKET_DURATION

public static final int DEFAULT_BUCKET_DURATION

default duration in seconds

See Also:

• Constant Field Values

DEFAULT_BUCKET_REQUESTS

public static final int DEFAULT_BUCKET_REQUESTS

default number of requests per duration

See Also:

• Constant Field Values

DEFAULT_ENFORCE

public static final boolean DEFAULT_ENFORCE

default value for enforce

See Also:

• Constant Field Values

DEFAULT_STATUS_CODE

public static final int DEFAULT_STATUS_CODE

default status code to return if requests per duration exceeded

See Also:

• Constant Field Values

DEFAULT_STATUS_MESSAGE

public static final String DEFAULT_STATUS_MESSAGE

default status message to return if requests per duration exceeded

See Also:

• Constant Field Values

RATE_LIMIT_ATTRIBUTE_COUNT

public static final String RATE_LIMIT_ATTRIBUTE_COUNT

request attribute that will contain the number of requests per duration

See Also:

• Constant Field Values

Constructor Details

RateLimitFilter

public RateLimitFilter()

Method Details

setBucketDuration

public void setBucketDuration(int bucketDuration)

setBucketRequests

public void setBucketRequests(int bucketRequests)

setEnforce

public void setEnforce(boolean enforce)

setStatusCode

public void setStatusCode(int statusCode)

setStatusMessage

public void setStatusMessage(String statusMessage)

setRateLimitClassName

public void setRateLimitClassName(String rateLimitClassName)

isConfigProblemFatal

protected boolean isConfigProblemFatal()

Description copied from class: FilterBase

Determines if an exception when calling a setter or an unknown configuration attribute triggers the failure of the this filter which in turn will prevent the web application from starting.

Overrides:

isConfigProblemFatal in class FilterBase

Returns:

true if a problem should trigger the failure of this filter, else false

init

public void init(FilterConfig filterConfig)
          throws ServletException

Description copied from class: FilterBase

Iterates over the configuration parameters and either logs a warning, or throws an exception for any parameter that does not have a matching setter in this filter.

Specified by:

init in interface Filter

Overrides:

init in class FilterBase

Parameters:

filterConfig - The configuration information associated with the filter instance being initialised

Throws:

ServletException - if FilterBase.isConfigProblemFatal() returns true and a configured parameter does not have a matching setter

doFilter

public void doFilter(ServletRequest request,
 ServletResponse response,
 FilterChain chain)
              throws IOException,
ServletException

Description copied from interface: jakarta.servlet.Filter

The doFilter method of the Filter is called by the container each time a request/response pair is passed through the chain due to a client request for a resource at the end of the chain. The FilterChain passed in to this method allows the Filter to pass on the request and response to the next entity in the chain.

A typical implementation of this method would follow the following pattern:-
1. Examine the request
2. Optionally wrap the request object with a custom implementation to filter content or headers for input filtering
3. Optionally wrap the response object with a custom implementation to filter content or headers for output filtering
4. a) Either invoke the next entity in the chain using the FilterChain object (chain.doFilter()),
4. b) or not pass on the request/response pair to the next entity in the filter chain to block the request processing
5. Directly set headers on the response after invocation of the next entity in the filter chain.

Parameters:

request - The request to process

response - The response associated with the request

chain - Provides access to the next filter in the chain for this filter to pass the request and response to for further processing

Throws:

IOException - if an I/O error occurs during this filter's processing of the request

ServletException - if the processing fails for any other reason

destroy

public void destroy()

Description copied from interface: jakarta.servlet.Filter

Called by the web container to indicate to a filter that it is being taken out of service. This method is only called once all threads within the filter's doFilter method have exited or after a timeout period has passed. After the web container calls this method, it will not call the doFilter method again on this instance of the filter.

This method gives the filter an opportunity to clean up any resources that are being held (for example, memory, file handles, threads) and make sure that any persistent state is synchronized with the filter's current state in memory. The default implementation is a NO-OP.

getLogger

protected Log getLogger()

Specified by:

getLogger in class FilterBase