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Knot.x HTTP Server

Server is essentially a "heart" of Knot.x. It's scalable (vertically and horizontally), plugable (easy to extend), fault-tolerant and highly efficient reactive server based on Vert.x.

Like any HTTP server, Knot.x HTTP Server allows you to define supported routes. Defining routes and security is done with Open API 3 standard.

Knot.x Server enables plugging in custom behaviour for each supported route. Each defined path is processed by the chain of Handlers that reacts on the request and is able to shape the response.

server flow

Tree of content


You will find docs in the files inside each of following modules:

How does it work

Knot.x HTTP Server is a verticle that listens for HTTP requests. It is responsible for handling the whole HTTP traffic that goes to the Knot.x instance.

Once the HTTP request comes to the Server following actions are happening:

  • Server checks if there is a routing path defined for the incoming request path and method. If no path supports this request, 404 Not Found is returned in the response.
  • Server checks whether a routing operation has been defined for the incoming request. If no handlers are defined in the operations for this route, 501 Not Implemented is returned in the response.
  • Handlers processing starts. In case of operation handler failure, failure handlers are triggered.
  • Handling is continued until any Handler ends (completes) the response. If none does, 500 Internal Server Error is returned.

How to configure

To run Knot.x HTTP Server, simply add an entry in the modules configuration:

modules = {
  server = "io.knotx.server.KnotxServerVerticle"

Details of the Knot.x HTTP Server can be configured with KnotxServerOptions in the configuration file:

config.server.options.config {
  # options defined here

More details about the module configuration can be found in Knot.x Launcher.

Http Server Options

HTTP options such as port, connection windows size, default version of ALPN (HTTP/2, HTTP/1) etc. can be configured with Vert.x HttpServerOptions.

E.g. following configuration specifies the port Server is listening at:

config.server.options.config {
  serverOptions {
    port = 8080

Server Port Configuration

Knot.x HTTP Server port can also be specified by the system property knotx.port that takes precedence over the value in the configuration file.

java -Dknotx.port=9999 ...

Dropping the requests

Knot.x Server implements the backpressure mechanism. It drops / rejects requests after exceeding a certain number of requests at a time. If Knot.x Server can NOT process incoming requests fast enough (the requests buffer limit has been reached), Server drops requests and responds with a configurable response code (by default 429, "Too Many Requests").

Dropping requests can be configured with DropRequestOptions

After the buffer slots are released, new requests will be accepted and finally processed.

That solution prevent OutOfMemoryError errors when there are too many requests (e.g. during the peak hours). Additionally response times should be more stable when system is under high stress.

Routing Specification

Knot.x Routing is defined with Open API 3 standard. routingSpecificationLocation is the path to the YAML Open API specification. It can be an absolute path, a local path or remote url (with HTTP).

config.server.options.config {
  routingSpecificationLocation = /openapi.yaml

Routing Operations

Routing Operation defines handlers and failure handlers involved in the processing of HTTP request for a specific operation defined in the Routing Specification (linking is done by operationId):

Open Api YAML config:

      operationId: my-example-operation

Routing Operations entry in Knot.x conf

config.server.options.config.routingOperations = ${routingOperations} [
    operationId = my-example-operation
    handlers = [
      # list of handlers that handles the request in chain
    failureHandlers = [
      # list of failure handlers

Routing Handler

Routing Handler is nothing else than a basic Vert.x Handler that operate on the RoutingContext. You may find more information about it in the API docs. Each handler is configured with Routing Handler Options.

Routing Order

Knot.x server makes use of the OpenAPI3RouterFactory in order to combine OpenAPI routes specification with configured handlers. According to OpenAPI3RouterFactory docs, handlers are loaded in this order:

  1. Body handler (Customizable with this#setBodyHandler(BodyHandler)
  2. Custom global handlers configurable with this#addGlobalHandler(Handler)
  3. Global security handlers defined in upper spec level
  4. Operation specific security handlers
  5. Generated validation handler
  6. User handlers or "Not implemented" handler

Also, operations in the server are mounted in the definition order inside yaml specification.

Routing Security

Security for each operation defined in the Open API specification is implemented in a form of AuthHandlers. In order to add security for the operation, you need to implement AuthHandlerFactory that provides AuthHandler of a proper type.

Example security setup

Open Api YAML config:

      operationId: my-example-operation
          - myExampleBasicAuth: []
      type: http
      scheme: basic

Routing Operations entry in Knot.x conf

config.server.options.config.securityHandlers = [
    schema = myExampleBasicAuth
    factory = myBasicAuthHandlerFactory
    config = {
      # any config passed to the AuthHandler

Also, you need to implement and register AuthHandlerFactory. For the example above:

  • name would be myBasicAuthHandlerFactory

Global Handlers

Global Handlers defines handlers that will be applied before any routing operation.

Please note that you should not add a body handler inside that list. If you want to modify the body use routing operation handlers.

config.server.options.config.globalHandlers = [
    name = myGlobalHandler
    config {
      // some configuration passed via factory to the handler

Each handler is specified with Routing Handler Options.

Access Logs

To log every request incoming to the Knot.x HTTP Server setup LoggerHandler as a globalHandler. Use loggerHandler factory and Access Log Options structure in order to configure it to your needs.

config.server.options.config.globalHandlers = [
    name = loggerHandler
    config {
      immediate = true
      format = DEFAULT

By default, access logs are logged to the knotx-access.log in the logs directory. To find more about default logger configuration, please see Knot.x Launcher logback settings.

Of course you may also use loggerHandler factory to log access to only specific routes via routing operation.


HTTP Server that handles all incoming HTTP requests and routes the traffic using OpenAPI specs




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