Configuring The Webserver Service

The webserver section in your Trapperkeeper configuration files configures an embedded HTTP server inside trapperkeeper.

host

This sets the hostname to listen on for unencrypted HTTP traffic. If not supplied, we bind to localhost, which will reject connections from anywhere but the server process itself. To listen on all available interfaces, use 0.0.0.0.

port

This sets what port to use for unencrypted HTTP traffic. If not supplied, but host is supplied, a value of 8080 will be used. If neither host nor port is supplied, we won't listen for unencrypted traffic at all.

acceptor-threads

This sets the number of threads that the webserver will dedicate to accepting socket connections for unencrypted HTTP traffic. Defaults to the number of virtual cores on the host divided by 8, with a minimum of 1 and maximum of 4.

selector-threads

This sets the number of selectors that the webserver will dedicate to processing events on connected sockets for unencrypted HTTPS traffic. Defaults to the minimum of: virtual cores on the host divided by 2 or max-threads divided by 16, with a minimum of 1.

max-threads

This sets the maximum number of threads assigned to responding to HTTP and/or HTTPS requests for a single webserver, effectively changing how many concurrent requests can be made at one time. Defaults to 200.

Each webserver instance requires a minimum number of threads in order to boot properly. The minimum number is calculated as:

(number of "acceptor-threads" for each port) +
(number of "selector-threads" for each port) +
(number of "reserved-threads" for each port) +
2 "worker" threads

Reserved threads are unconfigurable and default to the minimum of the number of virtual cores or max-threads divided by 10, with a minimum of one thread allocated.

Because reserved threads (and if not explicitly configured, selector threads) scale with max-threads, lowering the max-threads will cause fewer resources to be allocated to handling reqeusts on each port down to a threshold calculable by the forumalas above.

If the configured value for max-threads is less than the minimum required value, server startup will fail with an IllegalStateException, with a message containing the words "Insufficient configured threads".

Note that each web request must be processed on a "worker" thread which is separate from the acceptor and selector threads. "1" is the minimum number of worker threads required to process incoming web requests. The max-threads value should be large enough that the server can allocate all of the selector and acceptor threads that it needs and yet still have a sufficient number of worker threads left over for handling concurrent web requests.

queue-max-size

This can be used to set an upper-bound on the size of the worker queue that the web server uses to temporarily store incoming client connections before they can be serviced. This value defaults to the maximum value of a 32-bit signed integer, 2147483647. A request which is rejected by the web server because the queue is full would be seen by the client as having initially connected to the server socket at the TCP layer but having been closed almost immediately afterward by the server with no HTTP layer response body.

request-body-max-size

This sets the maximum size, in bytes, of the body for an HTTP request. The size of the request body is determined from the value for the request's HTTP Content-Length header. If the Content-Length exceeds the configured value, Jetty will return an HTTP 413 Error response. If this setting is not configured and/or the request does not provide a Content-Length header, Jetty will pass the request through to underlying handlers (bypassing Content-Length evaluation).

request-header-max-size

This sets the maximum size of an HTTP Request Header. If a header is sent that exceeds this value, Jetty will return an HTTP 431 Error response. This defaults to 8192 bytes, and only needs to be configured if an exceedingly large header is being sent in an HTTP Request.

so-linger-seconds

This setting has been removed. The option used in Jetty no longer attempts to set the SO_LINGER for the socket as of v9.4.12.

The Jetty maintainers discovered this option has undefined behavior on non-blocking connections (and all underlying connections became non-blocking in Jetty 9.0).

The actual behavior, though undefined by the Java spec, also changes between Java versions (so a user on Java 8 will see different behavior on Java 11) and has been reported to the Jetty community as a source of bugs on some platforms.

idle-timeout-milliseconds

This optional setting can be used to control how long Jetty will allow a connection to be held open by a client without any activity on the socket. If a connection is idle for longer than this value, Jetty will forcefully close it from the server side. Jetty's default value for this setting is 30 seconds. Note that Jetty will not automatically close the connection if the idle timeout is reached while Jetty is still actively processing a client request.

ssl-host

This sets the hostname to listen on for encrypted HTTPS traffic. If not supplied, we bind to localhost. To listen on all available interfaces, use 0.0.0.0.

ssl-port

This sets the port to use for encrypted HTTPS traffic. If not supplied, but ssl-host is supplied, a value of 8081 will be used for the https port. If neither ssl-host nor ssl-port is supplied, we won't listen for encrypted traffic at all.

ssl-acceptor-threads

This sets the number of threads that the webserver will dedicate to accepting socket connections for encrypted HTTPS traffic. Defaults to the number of virtual cores on the host divided by 8, with a minimum of 1 and maximum of 4.

ssl-selector-threads

This sets the number of selectors that the webserver will dedicate to processing events on connected sockets for encrypted HTTPS traffic. Defaults to the number of virtual cores on the host divided by 2, with a minimum of 1 and maximum of 4. The number of selector threads actually used by Jetty is twice the number of selectors requested. For example, if a value of 3 is specified for the ssl-selector-threads setting, Jetty will actually use 6 selector threads.

ssl-cert

This sets the path to the server certificate PEM file used by the web service for HTTPS. During the SSL handshake for a connection, certificates extracted from this file are presented to the client for the client's use in validating the server. This file may contain a single certificate or a chain of certificates ordered from the end certificate first to the most-root certificate last. For example, a certificate chain could contain:

• An end certificate
• An intermediate CA certificate with which the end certificate was issued
• A root CA certificate with which the intermediate CA certificate was issued

In the PEM file, the end certificate should appear first, the intermediate CA certificate should appear second, and the root CA certificate should appear last.

If a chain is present, it is not required to be complete. If a path has been specified for the ssl-cert-chain setting, the server will construct the cert chain starting with the first certificate found in the ssl-cert PEM and followed by any certificates in the ssl-cert-chain PEM. In the latter case, any certificates in the ssl-cert PEM beyond the first one would be ignored.

Note: This setting overrides the alternate configuration settings keystore and key-password.

ssl-cert-chain

This sets the path to a PEM with CA certificates for use in presenting a client with the server's chain of trust. Certs found in this PEM file are appended after the first certificate from the ssl-cert PEM in the construction of the certificate chain. This is an optional setting. The certificates in the ssl-cert-chain PEM file should be ordered from the least-root CA certificate first to the most-root CA certificate last. For example, a certificate chain could contain:

• An end certificate
• An intermediate CA certificate with which the end certificate was issued
• A root CA certificate with which the intermediate CA certificate was issued

The end certificate should appear in the ssl-cert PEM file. In the ssl-cert-chain PEM file, the intermediate CA certificate should appear first and the root CA certificate should appear last.

The chain is not required to be complete.

Note: This setting overrides the alternate configuration settings keystore and key-password.

ssl-key

This sets the path to the private key PEM file that corresponds with the ssl-cert, it used by the web service for HTTPS.

Note: This setting overrides the alternate configuration settings keystore and key-password.

ssl-ca-cert

This sets the path to the CA certificate PEM file used for client authentication. The PEM file may contain one or more CA certificates. Authorized clients must have been signed - either directly or via an intermediate CA - using one of the CA certificates in the PEM file.

Note: This setting overrides the alternate configuration settings truststore and trust-password.

keystore

This sets the path to a Java keystore file containing the key and certificate to be used for HTTPS.

key-password

This sets the passphrase to use for unlocking the keystore file.

truststore

This describes the path to a Java keystore file containing the CA certificate(s) for your infrastructure.

trust-password

This sets the passphrase to use for unlocking the truststore file.

cipher-suites

Optional. The cryptographic ciphers to allow for incoming SSL connections. This may be formatted either as a list (in a HOCON configuration file) or a comma-separated string. Valid names are listed in the official JDK cryptographic providers documentation; you'll need to use the all-caps cipher suite name.

If not supplied, trapperkeeper uses this list of cipher suites:

• TLS_DHE_RSA_WITH_AES_128_GCM_SHA256
• TLS_DHE_RSA_WITH_AES_256_GCM_SHA384
• TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
• TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
• TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
• TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384

ssl-protocols

Optional. The protocols to allow for incoming SSL connections. This may be formatted either as a list (in a HOCON configuration file) or a comma-separated string. Valid names are listed in the official JDK cryptographic protocol documentation; you'll need to use the names with verbatim capitalization. For example: TLSv1, TLSv1.1, TLSv1.2.

If not supplied, trapperkeeper uses this list of SSL protocols:

• TLSv1.2

When running on Java 11 users are encouraged to add TLSv1.3 to the list of supported protocols.

client-auth

Optional. This determines the mode that the server uses to validate the client's certificate for incoming SSL connections. One of the following values may be specified:

• need - The server will request the client's certificate and the certificate must be provided and be valid. The certificate must have been issued by a Certificate Authority whose certificate resides in the truststore.

• want - The server will request the client's certificate. A certificate, if provided by the client, must have been issued by a Certificate Authority whose certificate resides in the truststore. If the client does not provide a certificate, the server will still consider the client valid.

• none - The server will not request a certificate from the client and will consider the client valid.

If a value is not provided for this setting, need will be used as the default value.

ssl-crl-path

Optional. This describes a path to a Certificate Revocation List file. Incoming SSL connections will be rejected if the client certificate matches a revocation entry in the file.

allow-renegotiation

Optional. This controls whether the web server will allow client initiated SSL/TLS renegotiations. By default this will be disabled since allowing client to renegotiate is a vulnerability causing denial of service and information disclosure in certain cases. It can be over-ridden by setting this parameter to true.

static-content

Optional. This is a list of static content to be added to the server as context handlers during initialization. Each item in this list should be a map containing two keys. The first, resource, is the path to the resource you want added as a context handler (the equivalent of the base-path argument of the add-context-handler service function). The second, path, is the URL endpoint at which you want to mount the context handler (the equivalent of the context-path argument of the add-context-handler service function).

For example, say you have a web-assets directory containing a file called image.jpg. If your configuration were like so:

webserver: {
  port: 8080
  static-content: [{resource: "./web-assets"
                    path:     "/assets"}]
}

Then the static content in the web-assets directory would be mounted at the URL endpoint "/assets" on your server during initialization, and you could access the contents of image.jpg by visiting "http://localhost:8080/assets/image.jpg".

By default, symbolic links will not be served by the Jetty9 Webservice. However, if you have a symbolic link that you want to serve as static content, you can add an extra option, follow-links, to the specification for a piece of static content. The value of this should be a boolean, and if set to true, symbolic links will be served.

For example, say that you have a symbolic link in your web-assets directory, image-link, that links to the image.jpg file. If you want this to be served, you would configure your static content like so:

webserver: {
  port: 8080
  static-content: [{resource: "./web-assets"
                    path:     "/assets"
                    follow-links: true}]
}

Since follow-links is set to true, image-link will now be served, and can be accessed by visiting "http://localhost:8080/assets/image-link".

gzip-enable

Optional. This controls whether or not the webserver could compress the response body for any request using Gzip encoding. A value of false would prevent the server from using Gzip encoding the response body for all requests. If this option is not specified or is specified with a value of true, the webserver "could" Gzip encode the response body.

Note that in order for Gzip encoding to be used, a client would also need to include in the request an "Accept-Encoding" HTTP header containing the value "gzip". The webserver also may use other heuristics to avoid Gzip encoding the response body independent of the configuration of this setting. For example, the webserver may skip compression for a sufficiently small response body.

access-log-config

Optional. This is a path to an XML file containing configuration information for the Logback-access module. If present, a logger will be set up to log information about any HTTP requests Jetty receives according to the logging configuration, as long as the XML file pointed to exists and is valid. Information on configuring the Logback-access module is available here.

An example configuration file can be found here. This example configures a FileAppender that outputs to a file, access.log, in the dev-resources directory. The pattern element configures the output format to match the Apache Combined Log Format. See the Logback access layout documentation for a list of other items that can be added to the pattern element.

TrapperKeeper configures the Logback-access library with additional support for the SLF4J Mapped Diagnostic Context (MDC). This support allows the %X and %mdc conversion words to be used in the Logback-access pattern which behave as described in the docs for Logback-classic. Jetty is configured to clear any items added to the MDC at the end of each request so that incorrect data won't show up in subsequent requests that are handled by the same worker thread.

shutdown-timeout-seconds

Optional. This is an integer representing the desired graceful stop timeout in seconds. Defaults to 30 seconds.

post-config-script

Optional. This setting is for advanced use cases only, and is intended for debugging purposes. You can use it to modify low-level Jetty settings that are not directly exposed in our normal configuration options. In most cases, if you find yourself using this, it is an indicator that we need to expose additional settings directly in our main configuration (so please let us know!). Also, the implementation details of this setting may change between releases.

If you do need to use this, you can set the value to a String containing some Java code that should be executed against the Jetty Server object. This object will be injected into the scope of your code in a variable named server.

Here is a pathological example that shows how you could change the port that your server listens on (which you could achieve in a much simpler fashion by using the existing port setting; this example is only for the purposes of illustration):

post-config-script: "import org.eclipse.jetty.server.ServerConnector;
                     ServerConnector c = (ServerConnector)(server.getConnectors()[0]);
                     c.setPort(10000);"

For more info on the Jetty Server object model, see the Jetty Javadocs.

Configuring multiple webservers on isolated ports

It is possible to configure multiple webservers on isolated ports within a single Jetty9 webservice. In order to configure multiple webservers, change the webserver section of your Trapperkeeper configuration files to be a nested map. Each key in this map is the id of a server, and its value is the configuration for that server.

For example, say you wanted to configure two servers on localhost, one on port 9000 and one on port 10000. The webserver section of your configuration file would look something like this:

webserver: {
    bar: {
        host: localhost
        port: 9000
    }

    foo: {
        host: localhost
        port: 10000
    }
}

This configuration would cause the Jetty9 service to create two different Jetty servers on isolated ports. You can then specify which server you would like to add handlers to when calling the Jetty9 service functions, and they will be added to the server you specify.

Please note that, with the above configuration, you MUST specify a server-id when calling a service function, or else the operation will fail. If you would like to have a multi-server configuration and NOT specify a server-id when calling some service functions, you can optionally specify a default server in your configuration file. Then, if no server-id is specified when performing an operation, the operation will automatically be performed on the default server.

To specify a default server, add a :default-server key with a value of true to the configuration information for one of your servers in your trapperkeeper configuration. For example:

webserver: {
    bar: {
        host:           localhost
        port:           9000
        default-server: true
    }

    foo: {
        host: localhost
        port: 10000
    }
}

The above configuration would set up two servers as in the previous example, except the server with id :bar would be set as the default server. Calling a service function without specifying a server-id will cause the operation to be performed on the server with id :bar.

Please note that only one server can be specified as the default server. Please also note that setting a default server is optional. It is only required if you are planning to call a service function without passing in a server-id in a multi-server set-up.

Note that you are NOT limited to two servers and can configure more according to your needs.

Also note that you can still set the webserver section of your configuration to be an un-nested map containing a single webserver configuration, like so

webserver: {
    host: localhost
    port: 9000
}

In this case, the Jetty9 Service will simply create a single webserver and give it id :default, and will automatically make this server the default server.

jmx-enable

Optional. When enabled this setting will register the Jetty 9 MBeans so they are visible via JMX. Useful for monitoring the state of your Jetty 9 instance while it is running; for monitoring and debugging purposes. Defaults to true.