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Design for Azure Management Libraries for Java

Namespace

Packages for Azure services are named as:

com.azure.resourcemanager.<service>

Within each package:

  • <package> contains manager class for Azure service, as well as root client and client builder.
  • <package>.models contains all core model interfaces and classes.
  • <package>.fluent contains all client classes.
  • <package>.fluent.inner contains additional model classes.
  • <package>.implementation contains non-public classes. They are intended for internal use only.

In addition to packages for Azure services, a root package com.azure.resourcemanager is provided for the convenience of including all supported services.

Maven

Group ID is:

com.azure.resourcemanager

Artifact ID for Azure services are:

azure-resourcemanager-<service>

In addition to artifacts for Azure services, an artifact azure-resourcemanager is provided for the convenience of including all supported services.

Fluent interface

Azure Management Libraries for Java is object-oriented API for managing Azure resources.

There are 3 levels of object for Azure resource management.

Topmost, there is service API, e.g. ComputeManager for Azure compute service or AzureResourceManager for all supported services. Authentication is required to instantiate the service API.

Next, there is resource collection API, e.g. VirtualMachines to manage Azure virtual machine. It can be instantiated from service API, e.g. as computeManager.virtualMachines() or azure.virtualMachines().

Finally, there is resource instance, e.g. VirtualMachine as a client-side representation of Azure virtual machine.

Resource provision

A resource instance can be instantiated as:

  • Creating a new Azure resource from resource collection API, with method verb define till create, e.g.
VirtualMachine virtualMachine = computeManager.virtualMachines()
    .define(name)...create();
  • Getting an existing Azure resource from resource collection API, with method verb get or list, e.g.
VirtualMachine virtualMachine = computeManager.virtualMachines()
    .getByResourceGroup(resourceGroupName, name);

After a resource instance is instantiated, it can be modified as:

  • Updating the Azure resource, with method verb update till apply, e.g.
virtualMachine.update()...apply();

After the Azure resource served its purpose, it can be deleted as:

  • Deleting the Azure resource from resource collection API, with method verb delete, e.g.
computeManager.virtualMachines().deleteByResourceGroup(resourceGroupName, name);

It is important to note that the resource instance, as client-side representation of the Azure resource, could be outdated as the Azure resource on service being modified or deleted by Portal, CLI, other SDKs, or even another thread in the same Java application.

Lazy resource creation

Azure resource provision occurs when method verb create or apply is called.

Without calling create, the resource is a Creatable<T> instance, which can be provided to another resource as dependent resource, or be used in batch creation.

For any resource that accept another dependent resource, consider supporting following methods:

  • withNewResource(Creatable<T> resource) takes a Creatable<T> instance, and create it when provisioning current resource.
  • withNewResource(String name, Sku sku, ...) takes a few required parameters for the dependent resource, and create it automatically when provisioning current resource.
  • withExistingResource(T resource) takes the existing dependent resource.
  • withExistingResource(String id) or withExistingResource(SubResource resource) takes the resource ID of the existing dependent resource, if only the ID is required by current resource.

Action on resource

Other than management of life-cycle on Azure resource, resource collection API and resource instance supports action method, which could trigger change of state on the Azure resource.

Actions should be supported by resource API, e.g. virtualMachine.restart().

For actions that is frequently called, consider providing it in resource collection API as well, e.g. computeManager.virtualMachines().restart(resourceGroupName, name). This saves the request to initiate the resource instance.

List and pagination

The method verb list in resource collection API usually returns a PagedIterable<T> instance.

The results can be iterated by items, in a for-loop, or via forEach. Alternatively, the results can be iterated by pages, e.g.

computeManager.virtualMachines().list()
    .iterableByPage()
    .forEach(page -> ...);

It is worth noting that page is requested on demand. Therefore, after result found, it helps to break in for-loop, or to findFirst in stream, by avoiding unnecessary requests.

Also, there is no caching for requested pages or items in the PagedIterable<T> instance. Therefore, if you iterate PagedIterable<T> a second times, it will again request pages even if they are already iterated in the first iteration.

Conditional request

For services support ETag and conditional request, consider supporting following methods in define...create and update...apply:

  • withETagCheck() enables implicit ETag check, which fails creation if resource already exists on service, and fails modification if resource on service has been modified by others.
  • withETagCheck(String etag) enables explicit ETag check on update.

Exception

Exception on management of Azure resource is a ManagementException instance. Detail of the error is a ManagementError instance.

managementError.getCode() and managementError.getMessage() returns code and message of the error response.