Class 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.

    • Constructor Summary

      Constructors 
      Constructor Description
      RateLimitFilter()  
    • Method Summary

      All Methods Instance Methods Concrete Methods 
      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​(java.lang.String rateLimitClassName)  
      void setStatusCode​(int statusCode)  
      void setStatusMessage​(java.lang.String statusMessage)  
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Field Detail

      • 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 java.lang.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 java.lang.String RATE_LIMIT_ATTRIBUTE_COUNT
        request attribute that will contain the number of requests per duration
        See Also:
        Constant Field Values
    • Constructor Detail

      • RateLimitFilter

        public RateLimitFilter()
    • Method Detail

      • 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​(java.lang.String statusMessage)
      • setRateLimitClassName

        public void setRateLimitClassName​(java.lang.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 java.io.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:
        java.io.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.