Stateful Function applications are composed of one or more Modules
.
A module is a bundle of functions that are loaded by the runtime and available to be messaged.
Functions from all loaded modules are multiplexed and free to message each other arbitrarily.
Stateful Functions supports two types of modules: Embedded and Remote.
Embedded modules are co-located with, and embedded within, the Apache Flink® runtime.
This module type only supports JVM based languages and are defined by implementing the StatefulFunctionModule
interface.
Embedded modules offer a single configuration method where stateful functions are bound to the system based on their function type.
Runtime configurations are available through the globalConfiguration
, which is the union of all configurations in the applications flink-conf.yaml
under the prefix statefun.module.global-config
and any command line arguments passed in the form --key value
.
Embedded modules leverage Java’s Service Provider Interfaces (SPI) for discovery.
This means that every JAR should contain a file org.apache.flink.statefun.sdk.spi.StatefulFunctionModule
in the META_INF/services
resource directory that lists all available modules that it provides.
Remote modules are run as external processes from the Apache Flink® runtime; in the same container, as a sidecar, or other external location.
This module type can support any number of language SDK’s.
Remote modules are registered with the system via YAML
configuration files.
A remote module configuration consists of a meta
section and a spec
section.
meta
contains auxillary information about the module.
The spec
describes the functions contained within the module and defines their persisted values.
module.spec.functions
declares a list of function
objects that are implemented by the remote module.
A function
is described via a number of properties.
function.meta.kind
http
function.meta.type
<namespace>/<name>
.function.spec.endpoint
function.spec.states
function.spec.maxNumBatchRequests
address
before invoking backpressure on the system.function.spec.timeout