Tempesta FW

What it is?

Tempesta FW is a hybrid solution that combines a reverse proxy and a firewall at the same time. It accelerates Web applications and protects them against DDoS attacks and several Web application attacks.

Tempesta FW is built into Linux TCP/IP stack for better and more stable performance characteristics in comparison with TCP servers on top of common Socket API or even kernel sockets.

We do our best to keep the kernel modifications as small as possible. Current patch is just about 2,000 lines.

Prerequisites & Installation

Please see our Wiki for system requirements and installation procedures.

Build

To build the module you need to do the following steps:

• Download the patched Linux kernel or patch vanilla kernel on your own using linux-4.9.35.patch.

• Build, install, and then boot the kernel. Classic build and install procedure is used. For that, go to the directory with the patched kernel sources, make sure you have a correct .config file, and then do the following (<N> is the number of CPU cores on the system):

    make -j<N>
    make -j<N> modules
    make -j<N> modules_install
    make install
  

• Optionally, add kernel parameter tempesta_dbmem to the kernel command line. The value is the order of 2MB memory blocks reserved on each NUMA node for Tempesta database. Huge pages are used if possible. The default value is 8 which stands for 512Mb reserved on each NUMA node.

    tempesta_dbmem=1
  

• Run make to build Tempesta FW and Tempesta DB modules:

    $ cd tempesta && make
  

Run & Stop

Use tempesta.sh script to run and stop Tempesta. The script provides help information with --help switch. Usage example:

    $ ./scripts/tempesta.sh --start
    $ ./scripts/tempesta.sh --stop

Configuration

Tempesta is configured via plain-text configuration file.

The file location is determined by the TFW_CFG_PATH environment variable:

    $ TFW_CFG_PATH="/opt/tempesta.conf" ./scripts/tempesta.sh --start

By default, the tempesta_fw.conf from this directory is used.

See tempesta_fw.conf for the list of available configuration directives, options and their descriptions.

Listening address

Tempesta listens to incoming connections on specified address and port. The syntax is as follows:

listen <PORT> | <IPADDR>[:PORT] [proto=http|https];

IPADDR may be either IPv4 or IPv6 address. Host names are not allowed. IPv6 address must be enclosed in square brackets (e.g. "[::0]" but not "::0"). If only PORT is specified, then address 0.0.0.0 (but not [::1]) is used. If only IPADDR is specified, then default HTTP port 80 is used.

Tempesta opens one socket for each listen directive. Multiple listen directives may be defined to listen on multiple addresses/ports. If listen directive is not defined in the configuration file, then by default Tempesta listens on IPv4 address 0.0.0.0 and port 80, which is an equivalent to listen 80 directive.

Below are examples of listen directive:

listen 80;
listen 443 proto=https;
listen [::0]:80;
listen 127.0.0.1:8001;
listen [::1]:8001;

It is allowed to specify the type of listening socket via the proto. At the moment HTTP and HTTPS protos are supported. If no proto option was given, then HTTP is supposed by the default.

TLS/SSL support

Tempesta allows the use of TLS-encrypted HTTP connections (HTTPS). HTTPS traffic is terminated by Tempesta. Backend servers always receive unecrypted traffic.

It is required that public certificate and private key are configured as follows:

ssl_certificate /path/to/tfw-root.crt;
ssl_certificate_key /path/to/tfw-root.key;

Also, proto=https option is needed for the listen directive.

Self-signed certificate generation

In case of using a self-signed certificate with Tempesta, it's convenient to use OpenSSL to generate a key and a certificate. The following shell command can be used:

openssl req -nodes -new -x509 -keyout tfw-root.key -out tfw-root.crt

You'll be prompted to fill out several X.509 certificate fields. The values are the same for the subject and the issuer in a self-signed certificate. Use any valid values as you like.

The file tfw-root.key contains the private key, and the file tfw-root.crt contains the public X.509 certificate. Both are in PEM format. These files are used in Tempesta configuration as follows:

ssl_certificate /path/to/tfw-root.crt;
ssl_certificate_key /path/to/tfw-root.key;

Keep-alive timeout

Tempesta may use a single TCP connection to send and receive multiple HTTP requests/responses. The syntax is as follows:

keepalive_timeout <TIMEOUT>;

TIMEOUT is a timeout in seconds during which a keep-alive client connection will stay open in Tempesta. The zero value disables keep-alive client connections. Default value is 75.

Below are examples of keepalive_timeout directive:

keepalive_timeout 75;

Caching

Tempesta caches Web-content by default, i.e. works as reverse proxy. Configuration directive cache manages the cache befavior:

• 0 - no caching at all, pure proxying mode;
• 1 - cache sharding when each NUMA node contains independent shard of whole cache. This mode has the smallest memory requirements;
• 2 - (default) replicated mode when each NUMA node has whole replica of the cache. It requires more RAM, but delivers the highest performance.

cache_db specifies path to a cache database files. The PATH must be absolute and the directory must exist. The database file must end with .tbd. E.g. cache_db /opt/tempesta/db/cache.tdb is the right Tmpesta DB path. However, this is the only path pattern rather than real path. Tempesta creates per NUMA node database files, so if you have two processor packages on modern hardware, then the following files will be created (one for each processor package) for the example above:

    /opt/tempesta/db/cache0.tdb
    /opt/tempesta/db/cache1.tdb

cache_size defines size (in bytes, suffixes like 'MB' are not supported yet) of each Tempesta DB file used as Web cache storage. The size must be multiple of 2MB (Tempesta DB extent size). Default value is 268435456 (256MB).

cache_methods specifies the list of cacheable request methods. Responses to requests with these methods will be cached. If this directive is skipped, then the default cacheable request method is GET. Note that not all of HTTP request methods are cacheable by the HTTP standards. Besides, some request methods may be cachable only when certain additional restrictions are satisfied. Also, note that not all HTTP request methods may be supported by Tempesta at this time. Below is an example of this directive:

cache_methods GET HEAD;

Caching Policy

Caching policy is controlled by rules that match the destination URL agsinst the pattern specified in the rule and using the match operator specified in the same rule. The full syntax is as follows:

<caching policy> <OP> <string> [<string>];

<caching policy> directive can be one of the following:

• cache_fulfill - Serve the request from cache. If the response is not found in cache, then forward the request to a back end server, and store the response in cache to serve future requests for the same resource. Update the cached response when necessary.
• cache_bypass - Skip the cache. Simply forward the request to a server. Do not store the response in cache.

<string> is the anticipated substring of URL. It is matched against the URL in a request according to the match operator specified by <OP>. Note that the string must be verbatim. Regular expressions are not supported at this time.

The following <OP> keywords (match operators) are supported:

• eq - URL is fully equal to <string>.
• prefix - URL starts with <string>.
• suffix - URL ends with <string>.

Caching policy directives are processed strictly in the order they are defined in the configuration file. Below are examples of caching policy directives:

cache_fulfill suffix ".jpg" ".png";
cache_bypass suffix ".avi";
cache_bypass prefix "/static/dynamic_zone/";
cache_fulfill prefix "/static/";

Also, a special variant of wildcard matching is supported. It makes all requests and responses either use or skip the cache. It should be used with caution.

cache_fulfill * *;
cache_bypass * *;

Manual Cache Purging

Cached responses may be purged manually using the PURGE request method and the URL of the cached response. A typical use case is that when some content is changed on the upstream server, then a PURGE request followed by a GET request will update an appropriate entry in the cache.

This functionality is controlled with the following directives:

• cache_purge [invalidate]; - Defines the purge mode invalidate just makes the cache record invalid. The cached response may still be returned to a client under certain conditions. This is the default mode. Other modes will be added in future.
• cache_purge_acl <ip_address>; - Specifies the IP addresses of hosts that are permitted to send PURGE requests. PURGE requests from all other hosts will be denied. That makes this directive mandatory when cache_purge directive is specified. Multiple addresses are separated with white spaces.

<ip_address> can be an IPv4 or IPv6 address. An IP address can be specified in CIDR format where the address is followed by a slash character and the prefix (or mask) with the number of significant bits in the addresses. Below are examples of a valid IP address specification:

127.0.0.1
192.168.10.50/24
::ffff:c0a8:b0a
[::ffff:c0a8:a0a]
::ffff:c0a8:b0b/120
[::ffff:c0a8:b0b]/120

A PURGE request can be issued using any tool that is convenient. Below is just one example:

curl -X PURGE http://192.168.10.10/

Non-Idempotent Requests

The consideration of whether a request is considered non-idempotent may depend on specific application, server, and/or service. A special directive allows the definition of a request that will be considered non-idempotent:

nonidempotent <METHOD> <OP> <ARG>;

METHOD is one of supported HTTP methods, such as GET, HEAD, POST, etc. OP is a string matching operator, such as eq, prefix, etc. ARG is an argument for OP, such as /foo/bar.html, example.com, etc.

One or more of this directive may be specified. The directives apply to one or more locations as defined below in the Locations section.

If this directive is not specified, then a non-idempotent request in defined as a request that has an unsafe method.

Below are examples of this directive:

nonidempotent GET prefix "/users/";
nonidempotent POST prefix "/users/";
nonidempotent GET suffix "/data";

Locations

Location is a way of grouping certain directives that are applied only to that specific location. Location is defined by a string and a match operator that are used to match the string against URL in requests. The syntax is as follows:

location <OP> "<string>" {
	<directive>;
	...
	<directive>;
}

<OP> and <string> are specified the same way as defined in the [Caching Policy](#Caching Policy) section.

Multiple locations may be defined. Location directives are processed strictly in the order they are defined in the configuration file.

Only caching policy directives and the nonidempotent directive may currently be grouped by the location directive. The directives defined outside of any specific location are considered the default policy for all locations.

When locations are defined in the configuration, the URL of each request is matched against strings specified in the location directives and using the corresponding match operator. If a matching location is found, then caching policy directives for that location are matched against the URL.

In case there's no matching location, or there's no matching caching directive in the location, the default caching policy directives are matched against the URL.

If a matching caching policy directive is not found, then the default action is to skip the cache - do not serve requests from cache, and do not store responses in cache.

Below is an example of location directive definition:

cache_bypass suffix ".php";
cache_fulfill suffix ".mp4";

location prefix "/static/" {
	cache_bypass prefix "/static/dynamic_zone/";
	cache_fulfill * *;
}
location prefix "/society/" {
	cache_bypass prefix "/society/breaking_news/";
	cache_fulfill suffix ".jpg" ".png";
	cache_fulfill suffix ".css";
	nonidempotent GET prefix "/society/users/";
}

Server Load Balancing

Guide on configuring servers and load balancers can be found on the following Wiki pages:

• Servers: Tempesta's side,
• Servers: backend side,
• Load Balancing.

Sticky Cookie

Sticky cookie is a special HTTP cookie that is generated by Tempesta. It allows for unique identification of each client or can be used as challenge cookie for simple L7 DDoS mitigation when bots are unable to process cookies. It is also used for a load balancing.

When used, Tempesta sticky cookie is expected in HTTP requests. Otherwise, Tempesta asks in an HTTP response that sticky cookie is present in HTTP requests from a client. Default behaviour is that Tempesta sticky cookies are not used.

The use and behaviour of Tempesta sticky cookies is controlled by a single configuration directive that can have several parameters. The full form of the directive and parameters is as follows:

sticky [name=<COOKIE_NAME>] [enforce];

name parameter specifies a custom Tempesta sticky cookie name COOKIE_NAME for use in HTTP requests. It is expected that it is a single word without whitespaces. When not specified explicitly, a default name is used.

enforce parameter demands that Tempesta sticky cookie is present in each HTTP request. If it is not present in a request, a client receives HTTP 302 response from Tempesta that redirects the client to the same URI, and prompts that Tempesta sticky cookie is set in requests from the client.

Below are examples of Tempesta sticky cookie directive.

• sticky; Enable Tempesta sticky cookie. Default cookie name is used. Tempesta expects that Tempesta sticky cookie is present in each HTTP request. If it is not present, then Tempesta includes Set-Cookie header field in an HTTP response, which prompts that Tempesta sticky cookie with default name is set in requests from the client.

• sticky enforce; Enable Tempesta sticky cookie. Default cookie name is used. Tempesta expects that Tempesta sticky cookie is present in each HTTP request. If it is not present, Tempesta sends HTTP 302 response that redirects the client to the same URI and includes Set-Cookie header field, which prompts that Tempesta sticky cookie with default name is set in requests from the client.

• sticky name=__cookie__; Enable Tempesta sticky cookie. The name of the cookie is __cookie__. Tempesta expects that Tempesta sticky cookie is present in each HTTP request. If it is not present, then Tempesta includes Set-Cookie header field in an HTTP response, which prompts that Tempesta sticky cookie with the name __cookie__ is set in requests from the client.

• sticky name=__cookie__ enforce; Enable Tempesta sticky cookie. The name of the cookie is __cookie__. Tempesta expects that Tempesta sticky cookie is present in each HTTP request. If it is not present, Tempesta sends HTTP 302 response that redirects the client to the same URI and includes Set-Cookie header field, which prompts that Tempesta sticky cookie with the name __cookie__ is set in requests from the client.

Sticky cookie value is calculated on top of client IP, User-Agent, session timestamp and the secret used as a key for HMAC. sticky_secret config option sets the secret string used for HMAC calculation. It's desirable to keep this value in secret to prevent automatic cookies generation on attacker side. By default Tempesta generates a new random value for the secret on start. This means that all user HTTP sessions are invalidated on Tempesta restart. Maximum length of the key is 20 bytes.

sess_lifetime config option defines HTTP session lifetime in seconds. Default value is 0, i.e. unlimited life time. When HTTP session expires the client receives 302 redirect with new cookie value if enforced sticky cookie is used. This option doesn't affect sticky cookie expire time - it's a session, temporal, cookie.

Frang

Frang is a separate Tempesta module for HTTP DoS and DDoS attacks prevention. It uses static limiting and checking of ingress HTTP requests. The main portion of it's logic is at HTTP layer, so it's recommended that ip_block option (enabled by default) is used to block malicious users at IP layer.

Use -f command key to start Tempesta with Frang:

$ ./scripts/tempesta.sh -f --start

Frang has a separate section in the configuration file, "frang_limits". The list of available options:

• ip_block - if the option is switched on, then Frang will add IP addresses of clients who reaches the limits to filter_db table, so that the clients traffic will be dropped much earlier. See also Filter section.

• request_rate - maximum number of requests per second from a client;

• request_burst - maximum number of requests per fraction of a second;

• connection_rate - maximum number of connections per client;

• connection_burst - maximum number of connections per fraction of a second;

• concurrent_connections - maximum number of concurrent connections per client;

• client_header_timeout - maximum time for receiving the whole HTTP message header of incoming request;

• client_body_timeout - maximum time between receiving parts of HTTP message body of incoming request;

• http_uri_len - maximum length of URI part in a request;

• http_field_len - maximum length of a single HTTP header field of incoming request. This limit is helpful to prevent HTTP Response Splitting and other attacks using arbitrary injections in HTTP headers;

• http_body_len - maximum length of HTTP message body of incoming request;

• http_header_cnt - maximum number of HTTP header in a HTTP message;

• http_header_chunk_cnt - limit number of chunks in all headers for HTTP request;

• http_body_chunk_cnt - limit number of chunks for HTTP request body;

• http_host_required - require presence of Host header in a request;

• http_ct_required - require presence of Content-Type header in a request;

• http_ct_vals - the list of accepted values for Content-Type header;

• http_methods - the list of accepted HTTP methods;

Various back end servers may differ in interpretation of certain aspects of the standards. Some may follow strict standards, whereas others may allow a more relaxed interpretation. An example of this is the Host: header field. It must be present in all HTTP/1.1 requests. However, the Host: field value may be empty in certain cases. Nginx is strict about that, while Apache allows an empty Host: field value in more cases. This can present an opportunity for a DoS attack. Frang's http_host_required option should be used in this case. That would leave handling of the Host: header field to Tempesta. Invalid requests would be denied before they reach a back end server.

Filter

Let's see a simple example to understand Tempesta filtering.

Run Tempesta with Frang enabled and put some load onto the system to make Frang generate a blocking rule:

$ dmesg | grep frang
[tempesta] Warning: frang: connections max num. exceeded for ::ffff:7f00:1: 9 (lim=8)

::ffff:7f00:1 is IPv4 mapped loopback address 127.0.0.1. Frang's rate limiting calls the filter module that stores the blocked IPs in Tempesta DB, so now we can run some queries on the database (you can read more about tdbq):

# ./tdbq -a info

Tempesta DB version: 0.1.14
Open tables: filter

INFO: records=1 status=OK zero-copy

The table filter contains all blocked IP addresses.

Additional Directives

Tempesta has a number of additional directives that control various aspects of a running system. Possible directives are listed below.

• hdr_via [string]; - As an intermediary between a client and a back end server, Tempesta adds HTTP Via: header field to each message. This directive sets the value of the header field, not including the mandatory HTTP protocol version number. Note that the value should be a single token. Multiple tokens can be specified in apostrophes, however everything after the first token and a white space will be considered a Via: header field comment. If no value is specified in the directive, the default value is used.

Performance Statistics

Tempesta has a set of performance statistics counters that show various aspects of Tempesta operation. The counters and their values are self-explanatory. Performance statistics can be shown when Tempesta is loaded and running. Below is an example of the command to show the statistics, and the output:

$ cat /proc/tempesta/perfstat
SS pfl hits                             : 5836412
SS pfl misses                           : 5836412
Cache hits                              : 0
Cache misses                            : 0
Client messages received                : 2918206
Client messages forwarded               : 2918206
Client messages served from cache       : 0
Client messages parsing errors          : 0
Client messages filtered out            : 0
Client messages other errors            : 0
Clients online                          : 0
Client connection attempts              : 2048
Client established connections          : 2048
Client connections active               : 0
Client RX bytes                         : 309329836
Server messages received                : 2918206
Server messages forwarded               : 2918206
Server messages parsing errors          : 0
Server messages filtered out            : 0
Server messages other errors            : 0
Server connection attempts              : 8896
Server established connections          : 8896
Server connections active               : 32
Server connections schedulable          : 32
Server RX bytes                         : 11494813434

Also, there's Application Performance Monitoring statistics. These stats show the time it takes to receive a complete HTTP response to a complete HTTP request. It's measured from the time Tempesta forwards an HTTP request to a back end server, and until the time it receives an HTTP response to the request (the turnaround time). The times are taken per each back end server. Minimum, maximum, median, and average times are measured, as well as 50th, 75th, 90th, 95th, and 99th percentiles. A file per each back end server/port is created in /proc/tempesta/servers/ directory. The APM stats can be seen as follows:

# cat /proc/tempesta/servers/192.168.10.230\:8080 
Minimal response time           : 0ms
Average response time           : 4ms
Median  response time           : 3ms
Maximum response time           : 66ms
Percentiles
50%:    3ms
75%:    7ms
90%:    11ms
95%:    15ms
99%:    29ms

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