Dependency Injection in Nameko Matt Bennett ~ Senior Engineer ~ onefinestay 

Dependency Injection Design pattern whereby an object's dependencies are injected or passed by reference into it, rather than constructed by the object. c l a s s W i d g e t ( o b j e c t ) : d e f _ _ i n i t _ _ ( s e l f ) : s e l f . s e s s i o n = g e t _ d b _ s e s s i o n ( ) c l a s s W i d g e t ( o b j e c t ) : d e f _ _ i n i t _ _ ( s e l f , s e s s i o n ) : s e l f . s e s s i o n = s e s s i o n Pretty simple 

Nameko Python framework for building service- oriented software Bookings Payments Homes Open-source software Active development on GitHub 

Nameko out of the box Everything you need to do: AMQP RPC AMQP Pub-Sub Bookings Payments Homes 

Definitions Entrypoints To interact with a service Dependencies For the service to interact with external things 

Example Service f r o m n a m e k o . r p c i m p o r t r p c f r o m . d e p e n d e n c i e s i m p o r t d a t a b a s e _ c o n n e c t i o n c l a s s H e l l o S e r v i c e ( o b j e c t ) : d a t a b a s e = d a t a b a s e _ c o n n e c t i o n ( D B _ U R I ) @ r p c d e f h e l l o ( s e l f , n a m e ) : s e l f . d a t a b a s e . a d d ( n a m e ) r e t u r n " H e l l o , { } " . f o r m a t ( n a m e ) 

Running HelloService f r o m n a m e k o . c o n t a i n e r s i m p o r t S e r v i c e C o n t a i n e r c o n f i g = { ' A M Q P _ U R I ' : ' a m q p : / / g u e s t : g u e s t @ l o c a l h o s t : 5 6 7 2 / ' } c o n t a i n e r = S e r v i c e C o n t a i n e r ( H e l l o S e r v i c e , . . . , c o n f i g ) c o n t a i n e r . s t a r t ( ) . . . 

Worker Lifecycle 1. Entrypoint "fires" 2. Worker created 3. Dependencies injected 4. Execute method 5. Discard worker w o r k e r _ i n s t a n c e = H e l l o S e r v i c e ( ) w o r k e r _ i n s t a n c e . d a t a b a s e = H e l l o S e r v i c e . d a t a b a s e . i n j e c t ( ) r e s u l t = w o r k e r _ i n s t a n c e . h e l l o ( n a m e ) d e l w o r k e r _ i n s t a n c e 

Why do it this way? Simple service logic Complex application f r o m n a m e k o . r p c i m p o r t r p c f r o m . d e p e n d e n c i e s i m p o r t d a t a b a s e _ c o n n e c t i o n c l a s s H e l l o S e r v i c e ( o b j e c t ) : d a t a b a s e = d a t a b a s e _ c o n n e c t i o n ( D B _ U R I ) @ r p c d e f h e l l o ( s e l f , n a m e ) : s e l f . d a t a b a s e . a d d ( n a m e ) r e t u r n " H e l l o , { } " . f o r m a t ( n a m e ) Separation of concerns 

Unit Testing Testing a service in isolation f r o m m o c k i m p o r t c a l l f r o m n a m e k o . t e s t i n g . s e r v i c e s i m p o r t w o r k e r _ f a c t o r y h e l l o _ s v c = w o r k e r _ f a c t o r y ( H e l l o S e r v i c e ) a s s e r t h e l l o _ s v c . h e l l o ( " M a t t " ) = = " H e l l o , M a t t " a s s e r t h e l l o _ s v c . d a t a b a s e . a d d . c a l l _ a r g s _ l i s t = = [ c a l l ( " M a t t " ) ] f r o m n a m e k o . t e s t i n g . s e r v i c e s i m p o r t w o r k e r _ f a c t o r y d a t a b a s e = s e t ( ) h e l l o _ s v c = w o r k e r _ f a c t o r y ( H e l l o S e r v i c e , d a t a b a s e = d a t a b a s e ) a s s e r t h e l l o _ s v c . h e l l o ( " M a t t " ) = = " H e l l o , M a t t " a s s e r t d a t a b a s e = = { " M a t t " } 

Integration Testing Testing a service with something else Host services the "normal" way Restrict scope of interaction through dependencies 

Replace Injections f r o m n a m e k o . t e s t i n g . s e r v i c e s i m p o r t r e p l a c e _ i n j e c t i o n s c o n t a i n e r = S e r v i c e C o n t a i n e r ( B o o k i n g S e r v i c e , . . . ) p u b l i s h e r _ m o c k = r e p l a c e _ i n j e c t i o n s ( c o n t a i n e r , " h o m e s _ p u b l i s h e r " ) c o n t a i n e r . s t a r t ( ) . . . Bookings Payments Homes 

Worker Lifecycle All dependencies participate worker setup worker result worker teardown 

Nice Examples Log Aggregator Sentry Reporter Statsd Monitor 

Summary Dependency Injection Simple idea Separation of concerns Nameko Encourages explicit dependencies Provides nice testing tools And other goodies... Nameko Workshop -- Tomorrow 10:20, MADE room 

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