Create an API proxy from an OpenAPI Specification | Apigee Edge

In this tutorial, you'll learn how to create an Edge API proxy from an OpenAPI Specification using the Apigee Edge management UI. When you call the API proxy with an HTTP client, such as cURL, the API proxy sends the request to the Apigee mock target service.

About the Open API Initiative

"The Open API Initiative (OAI) is focused on creating, evolving and promoting a vendor neutral API Description Format based on the Swagger Specification." For more information about the Open API Initiative, see https://openapis.org.

An OpenAPI Specification uses a standard format to describe a RESTful API. Written in either JSON or YAML format, an OpenAPI Specification is machine readable, but is also easy for humans to read and understand. The specification describes such elements of an API as its base path, paths and verbs, headers, query parameters, operations, content types, response descriptions, and more. In addition, an OpenAPI Specification is commonly used to generate API documentation.

About the Apigee mock target service

The Apigee mock target service used in this tutorial is hosted at Apigee and returns simple data. It requires no API key or access token. In fact, you can access it in a web browser. Try it out by clicking the following:

http://mocktarget.apigee.net

The target service returns the greeting Hello, guest!

For information about the full set of APIs the mock target service supports, click on the following:

http://mocktarget.apigee.net/help

What you'll need

An Apigee Edge account. If you don't have an account, you can sign up by following the instructions at Creating an Apigee Edge account.
An OpenAPI Specification. In this tutorial, you'll use the mocktarget.yaml OpenAPI Specification which describes Apigee's mock target service, http://mocktarget.apigee.net. For more information, see https://github.com/apigee/api-platform-samples/tree/master/default-proxies/helloworld/openapi.
cURL installed on your machine to make API calls from the command line; or a web browser.

Create the API proxy

Edge

To create the API proxy from an OpenAPI Specification using the Edge UI:

Sign in to https://apigee.com/edge.
Click API Proxies in the main window.
Alternatively, you can select Develop > API Proxies in the left navigation bar.
Click + Proxy.
In the Create Proxy wizard, click Use OpenAPI Spec for the Reverse proxy (most common) template.
Click Import from URL and enter the following information:
- OpenAPI Spec URL: Path to the raw content on GitHub for the OpenAPI Specification in the URL field:
```
https://raw.githubusercontent.com/apigee/api-platform-samples/master/default-proxies/helloworld/openapi/mocktarget3.0.yaml
```
- Spec name: Name for the OpenAPI Specification, such as Mock Target.
  This name is used to store the OpenAPI Specification in the spec store. See Manage your specifications.

Click Import.

The Details page in the Create Proxy wizard displays. The fields are pre-populated using values defined in the OpenAPI Specification, as shown in the following

The following table describes the default values that are pre-populated using properties in the OpenAPI Specification. An excerpt of the OpenAPI Specification illustrating the properties used is shown following the table.

Field	Description	Default
Name	Name of the API proxy. For example: `Mock-Target-API`.	`title` property from the OpenAPI Specification with spaces replaced by dashes
Base path	Path component that uniquely identifies this API proxy within the organization. The public-facing URL of this API proxy is comprised of your organization name, an environment where this API proxy is deployed, and this base path. For example: `http://myorg-test.apigee.net/mock-target-api`	Name field content converted to all lower case
Description	Description of the API proxy.	`description` property from the OpenAPI Specification
Target (Existing API)	Target URL invoked on behalf of this API proxy. Any URL that is accessible over the open Internet can be used. For example: `http://mocktarget.apigee.net`	`servers` property from the OpenAPI Specification

The following provides an excerpt from the OpenAPI Specification showing the properties that are used to pre-populate the fields.

openapi: 3.0.0
info:
  description: OpenAPI Specification for the Apigee mock target service endpoint.
  version: 1.0.0
  title: Mock Target API
paths:
  /:
    get:
      summary: View personalized greeting
      operationId: View a personalized greeting
      description: View a personalized greeting for the specified or guest user.
      parameters:
        - name: user
          in: query
          description: Your user name.
          required: false
          schema:
            type: string
      responses:
        "200":
          description: Success
...
servers:
  - url: http://mocktarget.apigee.net
  - url: https://mocktarget.apigee.net
...

Edit the Description field as follows: API proxy for the Apigee mock target service endpoint.
Click Next.
On the Common policies page, under Security: Authorization ensure that Pass through (no authorization) is selected, and click Next:
On the Flows page, make sure all operations are selected.
Tip: Conditional flows are generated automatically from the operations that are defined within the paths object in the OpenAPI Specification. Conditional flows tell Edge, "When you see this, perform this logic." For example, when an API call is a GET on the /xml resource (the condition), transform the response to JSON (through a policy attached to the conditional flow). Only one flow executes per transaction—the first flow whose condition evaluates to true.
Click Next.
On the Virtual hosts page, select default and secure, and click Next.
On the Summary page, make sure the Test environment is selected under Optional Deployment and click Create and deploy:

Apigee creates your new API proxy and deploys it to your test environment:
Click Edit proxy to display the Overview page for the API proxy.

Classic Edge (Private Cloud)

To create the API proxy from an OpenAPI Specification using the Classic Edge UI:

Sign in to https://apigee.com/edge.
Click API Proxies in the main window.
Alternatively, you can select Develop > API Proxies in the left navigation bar.
Click + Proxy.
In the Create Proxy wizard, select Reverse proxy (most common) and click Use OpenAPI.
Click Import from a URL, enter a name for the OpenAPI Specification, and enter the path to the raw content on GitHub for the OpenAPI Specification in the URL field:

https://raw.githubusercontent.com/apigee/api-platform-samples/master/default-proxies/helloworld/openapi/mocktarget.yaml
Click Select.

Click Next.

The Details page in the Create Proxy wizard displays. The fields are pre-populated using values defined in the OpenAPI Specification, as shown in the following figure.

The following table describes the default values that are pre-populated using properties in the OpenAPI Specification. An excerpt of the OpenAPI Specification illustrating the properties used is shown following the table.

Field	Description	Default
Proxy Name	Name of the API proxy. For example: `Mock-Target-API`.	`title` property from the OpenAPI Specification with spaces replaced by dashes
Proxy Base Path	Path component that uniquely identifies this API proxy within the organization. The public-facing URL of this API proxy is comprised of your organization name, an environment where this API proxy is deployed, and this base path. For example: `http://myorg-test.apigee.net/mock-target-api`	Name field content converted to all lower case
Existing API	Target URL invoked on behalf of this API proxy. Any URL that is accessible over the open Internet can be used. For example: `http://mocktarget.apigee.net`	`servers` property from the OpenAPI Specification
Description	Description of the API proxy.	`description` property from the OpenAPI Specification

The following provides an excerpt from the OpenAPI Specification showing the properties that are used to pre-populate the fields.

openapi: 3.0.0
info:
  description: OpenAPI Specification for the Apigee mock target service endpoint.
  version: 1.0.0
  title: Mock Target API
paths:
  /:
    get:
      summary: View personalized greeting
      operationId: View a personalized greeting
      description: View a personalized greeting for the specified or guest user.
      parameters:
        - name: user
          in: query
          description: Your user name.
          required: false
          schema:
            type: string
      responses:
        "200":
          description: Success
...
servers:
  - url: http://mocktarget.apigee.net
  - url: https://mocktarget.apigee.net
...

Edit the Description field as follows: API proxy for the Apigee mock target service endpoint.
Click Next.
On the Flows page, make sure all operations are selected.
Tip: Conditional flows are generated automatically from the operations that are defined within the paths object in the OpenAPI Specification. Conditional flows tell Edge, "When you see this, perform this logic." For example, when an API call is a GET on the /xml resource (the condition), transform the response to JSON (through a policy attached to the conditional flow). Only one flow executes per transaction—the first flow whose condition evaluates to true.
Click Next.
On the Security page, select Pass through (none) as the security option, and click Next.
On the Virtual Hosts page, make sure all virtual hosts are selected and click Next.
On the Build page, make sure the test environment is selected, and click Build and Deploy.
On the Summary page, you see an acknowledgement that your new API proxy was created successfully and deployed to your test environment.
Click Mock-Target-API to display the Overview page for the API proxy.

Congratulations! You've created an API proxy from an OpenAPI Specification. Next you'll test it to see how it works.

Test the API proxy

You can test your Mock-Target-API API using cURL or a web browser.

In a terminal window, run the following cURL command. Substitute your organization name in the URL.

curl http://<org_name>-test.apigee.net/mock-target-api

Response

You should see the following response:

Hello, Guest!

Way to go! You've built a simple API proxy from an OpenAPI Specification and tested it.

Add an XML to JSON policy

Next, you'll add the XML to JSON policy to the View XML Response conditional flow that was generated automatically when you created the API proxy from the OpenAPI Specification. The policy will convert the target's XML response to a JSON response.

First, call the API so that you can compare the results with those received after you add the policy. In a terminal window execute the following cURL command. You're calling the target service's /xml resource, which natively returns a simple block of XML. Substitute your organization name in the URL.

curl http://<org_name>-test.apigee.net/mock-target-api/xml

Response

You should see the following response:

<root> 
  <city>San Jose</city> 
  <firstName>John</firstName> 
  <lastName>Doe</lastName> 
  <state>CA</state> 
</root>

Now let's do something that converts the XML response to JSON. Add the XML to JSON policy to the View XML Response conditional flow in the API proxy.

Click the Develop tab in the top right corner of the Mock-Target-API Overview page in the Edge UI.
In the left Navigator pane, under Proxy Endpoints > default, click the View XML Response conditional flow.
Click the bottom +Step button, corresponding to the Response for the flow.

The Add Step dialog opens to display a categorized list of all the policies that you can add.
Scroll to the Mediation category and select XML to JSON.
Keep the default values for Display Name and Name.
Click Add. The XML to JSON policy is applied to the response.
Click Save.

Now that you've added the policy, call the API again using cURL. Notice that you're still calling the same /xml resource. The target service still returns its block of XML, but now the policy in the API proxy will convert the response to JSON. Make this call:

curl http://<org_name>-test.apigee.net/mock-target-api/xml

Note that the XML response is converted to JSON:

{"root":{"city":"San Jose","firstName":"John","lastName":"Doe","state":"CA"}}

Congratulations! You have successfully tested the execution of a policy added to a conditional flow.