Question

How can I retrieve the number of API invocations? I know the data has to be somewhere because wso2 BAM shows piecharts with similar data…

I would like to get that number in a mediation sequencel; is that possible? Might this might be achieved via a DB-lookup?

Answer 1

The way how API Usage Monitoring in WSO2 API Manager works is, there is an API handler (org.wso2.carbon.apimgt.usage.publisher.APIUsageHandler) that gets invoked for each request and response passing through the API gateway. In this handler all pertinent information with regard to API usage is published to the WSO2 BAM server. The WSO2 BAM server persists this data in Cassandra database that is shipped with it. Then there is a BAM Toolbox that has been packaged with required analytic scripts written using Apache Hive that can be installed on the BAM server. These scripts would summarize the data periodically and persist the summarized data to an sql database. So the graphs and charts shown in the API Publisher web application are created using the summarized data from the sql database.

Now, if what you require is extractable from these summarized sql tables then i suppose the process is very straight forward. You could use the DBLookup mediator for this. But if some dimension of the data which you need has been lost due to the summarizing, then you will have a little more work to do.

You have two options.

1. The easiest approach which involves no coding at all would be to write a custom Hive script that suits your requirement and summarize data to a sql table. Then, like before use a DBLookup mediator to read the data. You can look at the existing Hive scripts that are shipped with the product to get an idea of how it is written.

2. If you dont want BAM in the picture, you still can do it with minimal coding as follows. The implementation class which performs the publishing is org.wso2.carbon.apimgt.usage.publisher.APIMgtUsageDataBridgeDataPublisher. This class implements the interface org.wso2.carbon.apimgt.usage.publisher.APIMgtUsageDataPublisher. The interface has three instace methods as follows.

   public void init()

   public void publishEvent(RequestPublisherDTO requestPublisherDTO)

   public void publishEvent(ResponsePublisherDTO responsePublisherDTO)

The init() method runs just once during server startup. Here is where you can add all your logic which is needed to bootstrap the class.
The publishEvent(RequestPublisherDTO) is where you publish request events and publishEvent(ResponsePublisherDTO) is where you publish response events. The DTO objects are encapsulated representations of the request and response data respectively.

What you will have to do is write a new implementation for this interface and configure it as the value for DataPublisherImpl property in api-manager.xml. To make things easier you can simply extends the exsiting org.wso2.carbon.apimgt.usage.publisher.APIMgtUsageDataBridgeDataPublisher, write your necessary logic to persist usage data to an sql database within the init(), publishEvent(RequestPublisherDTO) and publishEvent(ResponsePublisherDTO) and at the end of each method just call its respective super class method.
E.g. the overriding init() will call super().init(). This way you are only adding the neccessary code for your requirement, and leaving the BAM stat collection requirement to the super class.