tysonnorris commented on a change in pull request #2414: SPI approach for
pluggable implementations
URL:
https://github.com/apache/incubator-openwhisk/pull/2414#discussion_r130931297
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File path: docs/spi.md
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@@ -0,0 +1,89 @@
+# SPI extensions in OpenWhisk
+
+Alternate implementations of various components follow an SPI (Service
Provider Interface) pattern:
+* The pluggable component is defined as an Spi trait:
+```scala
+import whisk.spi.Spi
+trait ThisIsPluggable extends Spi { ... }
+```
+* Implementations implement the Spi trait
+```scala
+class TheImpl extends ThisIsPluggable { ... }
+class TheOtherImpl extends ThisIsPluggable { ... }
+```
+
+Runtime resolution of an Spi trait to a specific impl is provided by:
+* Akka Extensions - a service registry housed inside the ActorSystem
+* SpiModule - a way to define a factory for each impl, all of which are loaded
via ServiceLoader
+* application.conf - each SpiModule defines a config key used to indicate
which impl should be used at runtime
+
+# Example
+
+The process to create and use an SPI is as follows:
+
+## Define the Spi and impl(s)
+
+* create your Spi trait `YourSpi` as an extension of whisk.spi.Spi
+* create your impls as classes that extend `YourSpi`
+
+## Define the SpiModule(s) to load the impl(s)
+
+```scala
+class YourImplModule extends SpiModule[YourSpi]{
+ def getInstance = new YourImpl
+}
+```
+
+To use scaldi injectors to bind dependencies, use:
+```scala
+class YourImplModule extends SpiFactoryModule[YourSpi]{
+ def getInstance(implicit injector:Injector) = new
YourImpl(inject[SomeDependencyType])
+}
+```
+
+Note: To bind dependencies (must be done before first access of the Spi):
+```scala
+//bind config
+SharedModules.bind[WhiskConfig](whiskConfig)
+//bind an Spi instance
+SharedModules.bind[YourSpi](yourSpi)
Review comment:
yep, done
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