Simulating services

Set up

To simulate a service, you will need to have either captured some traffic (see the Capturing traffic section) or imported a service data file (see the Exporting and importing section).

Simulate a service

With Hoverfly running as a proxy

You will need to have your application or OS configured to use Hoverfly as a proxy (see the Installation and setup section).

Put Hoverfly into simulate mode. There are four ways of doing this:

1. Use hoverctl to start Hoverfly and set the mode to simulate:

   hoverctl start
   hoverctl mode simulate
   

2. Start Hoverfly without specifying the mode (Hoverfly starts in simulate mode by default)

   ./hoverfly
   

3. Ensure Hoverfly is running (in any mode), then select "simulate" in the Admin UI, which is available at http://${HOVERFLY_HOST}:8888 by default.

4. Ensure Hoverfly is running (in any mode), then make an API call:

   curl -H "Content-Type application/json" -X POST -d '{"mode":"simulate"}' http://${HOVERFLY_HOST}:8888/api/state
   

Provided you have previously captured traffic either using cURL or by running tests, you can now repeat the steps you took to capture traffic.

Instead of using the external service you captured, your application (or cURL) will now be using the Hoverfly simulation.

If you are running a test suite, you will probably notice that it runs much faster.

With Hoverfly running as a webserver

Put Hoverfly into simulate mode while it is running as a webserver. There are two ways to do this:

1. Use hoverctl to start Hoverfly as a webserver, and set the mode to simulate:

   hoverctl start webserver hoverctl mode simulate

2. Start Hoverfly with the -webserver flag and do not specify a mode (Hoverfly starts in simulate mode by default)

   ./hoverfly -webserver
   

NOTE: When running as a webserver, Hoverfly currently only supports simulate mode.

NOTE: Currently HTTPS is not supported when running Hoverfly as a webserver. HTTPS support when running as a webserver is on the roadmap.

Provided you have previously captured traffic either using cURL or by running tests with Hoverfly running as a proxy (or you have imported previously captured traffic - see the Exporting and importing section), Hoverfly can now be used instead of the external service you captured.

Since Hoverfly is simulating the service as a webserver rather than a proxy, you will need to substitute the host name of the service you captured with the host and port that the Hoverfly webserver is running on when you make a request.

For example, if you created a simulation by running the following command with Hoverfly running in capture mode as a proxy:

  curl http://my.host.com/api/health

You would need to run the following command with Hoverfly running in simulate mode as a webserver to get the captured response:

  curl http://${HOVERFLY_HOST}:8500/api/health

What is happening?

Hoverfly is no longer passing requests through to the external service. Instead, for each request it receives, it is returning a matched response from its cache. The cache is stored in memory, and persisted on disk in the requets.db file.

Next steps

Now you have simulated a service, you can use middleware to simulate network latency or failure, or manipulate data in the responses. Proceed to the Middleware section.

Alternatively, you can learn how to use synthesize mode to generate responses to requests on the fly. Proceed to the Creating synthetic services section.

Further reading

A detailed step-by-step guide to capturing traffic and creating a simulated service is available here:

Speeding up your slow dependencies

A guide on how to capture and simulate the Meetup API is available here:

Virtualizing the Meetup API