Mocks for microservice environments

Getting Started

Learning Videos

Config Syntax

Request Matching

Response Templating

Async Actors (Kafka etc.)

Performance & Chaos Testing

Remote Management


Configuration Syntax

Mockintosh supports JSON and YAML formats for the mock server configuration file.

The most important entities in the config file are: Service, Endpoint, Response:


There are two main aspects of endpoint configuration: matching and templating. Matching defines how to recognize request and pick the corresponding response template. Templating gives capabilities to configure different response fields, and also make responses to be dynamic.

Note: There is a JSONSchema of configuration syntax that is used to validate all configuration files. You can use that as a formal source of configuration syntax.

Defining Services

When defining services, the key property is port, which defines on which port the server will be available to requests. It is also a good practice to specify name property, which is just piece of string. You can configure one or multiple services at once. Here’s a minimalistic working example:

  - name: Catalogue API
    port: 8001
      - path: /
  - name: Cart API
    port: 8002
      - path: /

You can additionally specify hostname property to make service only respond to requests that contain specific Host HTTP header:

  - name: I'm like Google
    port: 8001
    hostname: www.google.com
      - path: /

Note: There is special MOCKINTOSH_FORCE_PORT environment variable that allows to force all services to have certain port (same for all) listened. This is meant for advanced use when “pick service by name” feature is used ( see here).

SSL Support

Enabling SSL for service is as easy as specifying ssl: true for it:

  - name: This requires 'https://' to be used by a client
    port: 443
    ssl: true

If you want to use SSL-enabled mock inside browser (or other client), you would need to add Mockintosh’s self-signed certificate into trusted store.

In case you want Mockintosh to use your SSL certificate and key, just provide it as below:

  - name: This requires 'https://' to be used by a client
    port: 443
    ssl: true
    sslCertFile: path/to/cert.crt
    sslKeyFile: path/to/cert.key

Multiple Services on Same Port (Virtual Hosts)

You can also serve multiple services from the same port number, if you provide them with different hostnames. This is handy when you serve multiple microservice mocks from single container:

  - name: "First service"
    hostname: "service1.example.com"
    port: 80
  - name: "Second service"
    hostname: "service2.example.com"
    port: 80

Fallback To

Service-level defined fallbackTo: "http://example.com/" option redirects every unhandled request to the specified base URL. e.g. for a path like /somepath the request would be redirected to http://example.com/somepath. The redirect in here does not mean returning 3xx but instead doing a server-side request and tunneling its response to the original requester. Such that the response of http://localhost:8001/somepath reflects the response of http://example.com/somepath.

Note: Timeout for such redirected requests is 30 seconds (504) and can be overridden with MOCKINTOSH_FALLBACK_TO_TIMEOUT environment variable.

Note: If the hostname in fallbackTo is an unresolved name then 502 will be returned.

If the management API is enabled, redirected requests are also logged as unhandled requests.

Note: You may want to play with your client’s /etc/hosts file contents when using virtual hosts.

Defining Endpoints

Endpoint is the main configuration entity of Mockintosh. Each service holds a list of endpoints, and uses that list for matching to requests. Once request is matched, the corresponding response is evaluated and returned.

Here is the full list of properties for endpoint configuration:

The response fields are described in detail in templating page, below is the quick list:

Here is config example with illustrations of several variants of endpoint definition:

  - port: 8000
      - path: /  # by default, method is GET, response is HTTP 200 with empty body

      - path: /api/action1
        method: "POST"
        response: "Simple string response" # can be just response content string

      - path: /api/action2
        response: # detailed specification allows controling status code and headers
          status: 201
          body: '@subdir/response.json'
            Content-Type: application/json

Note: Apart from numeric HTTP status codes, RST and FIN special values can be set in the status field to simulate the behavior of sudden TCP connection reset or close.

Multiple Responses

The response field under endpoint can be an array, too. If this field is an array then for each request the next item is taken for response. For example, considering the configuration below:

  - "@index.html"
  - headers:
      content-type: image/png
    body: "@subdir/image.png"
  - just some text
  1. request: index.html file is returned with Content-Type: text/html header.
  2. request: subdir/image.png image is returned with Content-Type: image/png header.
  3. request: just some text is returned with Content-Type: text/html header.
  4. request: index.html again and so on…

The looping can be disabled with setting multiResponsesLooped to false, in this case you will start getting HTTP 410 response after all items in response list are exhausted.

Tagged Responses

As part of advanced usage of Mockintosh, you can specify tag field on each of multi-response items. If tag is specified, the response is only considered if corresponding tag is set as “current” via current tag. Responses without tag attribute are always selected.

Here’s the example:

  - port: 8000
      - path: /some/path
          - tag: success-case
            status: 200
            body: Me working
          - tag: failure-case
            status: 503
            body: simulated outage


One can put a dataset field under endpoint to specify a list of key-value combinations to inject into response templating.

This field can be a string that starts with @ to indicate a path to an external JSON file like @subdir/dataset.json or an array:

  - var1: val1
  - var1: val2
response: 'dataset: {{var1}}'

This dataset is looped just like how Multiple responses are looped:

  1. request: dataset: val1 is returned.
  2. request: dataset: val2 is returned.
  3. request: dataset: val1 is returned.

The looping can be disabled with setting datasetLooped to false. In this case, on 3rd request, the endpoint returns 410 status code with an empty response body.

Global Settings

Under the globals section of config, you can specify headers that will be set for each response:

    X-Tenant-Id: "test-tenant"
    Content-Type: application/json

Automatic CORS (Cross-Origin Resource Sharing)

Mockintosh serves CORS pre-flight requests automatically for all defined endpoints, unless there is existing OPTIONS method endpoint in service configuration. The mock server will respond to such pre-flight requests with 204 status code.

For any request that has Origin header provided, the mock server will set Origin and Access-Control-Allow-Headers headers in the response according to the Origin and Access-Control-Request-Headers in the request headers. It will also set Access-Control-Allow-Methods header to DELETE, GET, HEAD, OPTIONS, PATCH, POST, PUT.

Advanced Templating with Jinja2

You can specifiy the templating engine on top of the file like templatingEngine: "Jinja2" or inside the response.

A response example that leverages Jinja2 templating and Faker is shown below:

  "users": [{% for n in range(request.queryString.total) %}
      "id": {{ random.int(10000, 100000) }},
      "firstName": "{{ fake.first_name() }}",
      "lastName": "{{ fake.last_name() }}",
      "friends": [{% for n in range(range(5) | random) %}
          "id": "{{ random.uuid4() }}"
        }{% if not loop.last %},{% endif %}
      {% endfor %}]
    }{% if not loop.last %},{% endif %}
  {% endfor %}],
  "total": {{ request.queryString.total }}

Performance/Chaos Profiles

It’s possible to define probabilistic performance profiles at the global-level to simulate server-side outages, response delays or errors. Suppose you have these performance profiles:

    ratio: 1
    delay: 1.5
      '200': 0.3
      '201': 0.1
      '400': 0.1
      '500': 0.2
      '503': 0.1
      PASS: 0.4
      RST: 0.2
      FIN: 0.1
    ratio: 0.3
    delay: 4.8

ratio: probablity of performance profile trigger to happen; ranges from 0.0 to 1.0. delay: reponse delay of the server in seconds. faults: probabilistic distribution of response status codes, reset connections (RST), close connections (FIN) and default status codes (PASS means ignore the fault)

A performance profile can be applied to a service, an endpoint or globally (in globals section) like: performanceProfile: profile1. performanceProfile field overrides the parent settings. Such that; service-level performance profile overrides the global-level, endpoint-level performance profile overrides both the service-level and global-level performance profiles.

If you pick profile1 for your service:

If you pick profile2 for your endpoint: