You need to create a custom trigger when you want to run your Azure Function as a reaction to your custom events. In the example we saw in the previous section, we would like to run our function when the temperature of a city rises by a threshold: exceeding the threshold represents our custom event.

You must create a custom binding, instead, when you want to interact with an external data source within your Azure Function and you want to demand at runtime the responsibility for the creation and life cycle management of the binding. In that case, your function receives the instance of the binding from the runtime and doesn't care about its creation or release.

In fact, you also can interact with an external source by creating your data access class inside the body of the Azure Function (for example, using the constructor), but in this scenario, you...