SCS ESI Sample
For Self-contained Systems multiple frontends need to be integrated. This sample shows how to do this. Varnish serves as a cache and also ESI (Edge Side Includes) are used to integrate multiple backends into one HTTP site.
This project creates a Docker setup with the complete systems based on Docker Compose and Docker Machine. The services are implemented in Java using Spring and Spring Cloud.
It uses two very simple SCS:
- Order to enter orders.
- Catalog to handle the items in the catalog.
How To Run
See How to run for details.
Remarks on the Code
The SCS are:
- scs-demo-esi-common provides web assets and common headers and footers for services. The microservice is written in Go and therfore has a small footprint. It uses Multi Stage Docker containers to compile the Go program in one Docker image and then copy over the result into a separate Docker image.
- scs-demo-esi-order does order processing. It outputs
esi:includein its HTML files to include the HTML snippets of
scs-demo-esi-common. These are interpreted by the Varnish web cache. This microservices is written in Java. It has an Java main application in src/test/java to run the microservice stand alone with some test data. However, the layout of the web page will be incomplete because the ESI includes are not handled.
Varnish interprets the ESIs. The
default.vcl in the directory
docker/varnish includes the configuration to enable this. It
defines two backends - one for each SCS. HTTP requests to
are mapped to the catalog SCS while the default is the order
SCS. The time to live for each item in the cache is 30s i.e. after
30 seconds an entry in the cache in invalidated and the call goes to
the backend. The grace is 15m: Even if the entry in the cache is
invalid it will be served for 15 more minutes of the backend is not
accessible. So if the backend crashes the cache can still provide
This is a technology demo. The coupling between the two components in this case is very tight - the integration is providing rather small components that are embedded in specific pages. In a real world architecture this should not be the case. Please refer to http://scs-architecture.org/ to better understand the architecture this should support.