What is Azure Orchestration and How Does it Work

Azure orchestration is a powerful tool that helps manage and automate complex tasks and workflows across multiple Azure services. It's essentially a conductor that coordinates all the different components of your application to ensure they work together seamlessly.

Azure orchestration is built on top of Azure Resource Manager (ARM), which provides a consistent and reliable way to manage and deploy resources in Azure. ARM is the foundation of Azure orchestration, allowing you to define and manage infrastructure and applications in a scalable and repeatable way.

By using Azure orchestration, you can automate tasks such as deploying and scaling applications, managing security and access, and monitoring performance and usage. This can help reduce errors, improve efficiency, and save time, allowing you to focus on more strategic and creative work.

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Azure orchestration is a powerful tool for managing distributed systems. It enables you to package, deploy, and manage scalable and reliable microservices.

Orchestrator functions are the core of Azure orchestration. They describe how actions are executed and the order in which actions are executed. Orchestrator functions can include activity functions, sub-orchestrations, waiting for external events, HTTP, and timers.

To write an orchestrator function, you must use ordinary code, but there are strict requirements on how to write the code. Specifically, orchestrator function code must be deterministic.

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Orchestrator functions are written using ordinary code, but there are strict requirements on how to write the code to ensure it runs correctly.

Orchestrator functions can interact with entity functions and can have many different types of actions, including activity functions, sub-orchestrations, waiting for external events, HTTP, and timers.

Determinism is a crucial aspect of orchestrator function code, and failing to follow these requirements can cause orchestrator functions to fail to run correctly.

The history of each orchestration is stored using an "event sourcing" technique, allowing for a detailed log of exactly what happened.

This log includes the input and output data of the orchestrator, as well as the input and output data of every single activity function or sub-orchestrator that was called along the way.

You can access the status of an orchestrator by calling the Get Instance Status API or using DurableOrchestrationClient.GetStatusAsync.

Orchestrator functions can call activity functions, but also other orchestrator functions, allowing you to build a larger orchestration out of a library of orchestrator functions.

Sub-orchestrations can also be run in parallel, enabling you to scale your applications and implement a CI/CD pipeline with ease.

Azure Kubernetes Service (AKS) is an open-source orchestration service for deploying, scaling, and managing containerized applications, streamlining Kubernetes management and deployment.

Azure Service Fabric is a distributed systems platform that enables you to package, deploy, and manage scalable and reliable microservices, providing comprehensive application lifecycle management capabilities.

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Entity functions define operations for reading and updating small pieces of state, often referred to as durable entities.

These stateful entities can be invoked from client functions or from orchestrator functions, just like orchestrator functions.

Entity functions can be invoked from client functions or from orchestrator functions.

Unlike orchestrator functions, entity functions do not have any specific code constraints.

Entity functions manage state explicitly rather than implicitly representing state via control flow.

Entity functions and related functionality is only available in Durable Functions 2.0 and above.

Client functions can be triggered by an orchestration trigger binding or an entity trigger binding, which react to messages enqueued into a task hub.

Orchestrator and entity functions can't be triggered directly from the Azure Portal, so you need to use a client function to start them.

A client function is any non-orchestrator function that uses the durable client output binding. This includes HTTP-triggered functions and Azure Event Hub triggered functions.

The durable client binding is used to interact with running orchestrations and entities, allowing you to query, terminate, and raise events to them.

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Batch is a cloud-based job scheduling service that parallelizes and distributes the processing of large volumes of data across many computers.

It's particularly useful for running large-scale parallel and high-performance computing (HPC) batch jobs efficiently in Azure.

You can scale out compute resources to achieve high throughput easily with Batch.

This is especially helpful for tasks that require heavy computation, such as media rendering and Monte Carlo simulations.

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Reliability and History are two key aspects of Azure Orchestration that are often overlooked, but are crucial for building robust and scalable applications.

The Durable Task Framework uses an append-only store to record the full series of actions an orchestration takes, ensuring eventual consistency for transactional data and full audit trails and history. This is achieved through event sourcing, which transparently commits new actions to storage, updating the execution history of the orchestration instance.

The framework also replays the execution history to rebuild the local state of the orchestrator function, ensuring that it can be unloaded from memory until there is more work for it to do. This is done by consulting the execution history of the current orchestration, where it finds that the activity function has already executed and yielded a result.

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Here are some key benefits of the Durable Task Framework's reliability and history features:

The Durable Task Framework also stores the history of each function orchestration, which grows continuously as long as the orchestrator function continues to schedule new work. This history is stored using an "event sourcing" technique, allowing for a detailed log of exactly what happened, including input and output data of the orchestrator and activity functions.

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Orchestrator functions maintain their execution state reliably through the event sourcing design pattern, which records the full series of actions an orchestration takes in an append-only store.

This approach has many benefits, including increased performance, scalability, and responsiveness. You also get eventual consistency for transactional data and full audit trails and history.

The Durable Task Framework uses this pattern transparently, committing new actions to storage and updating the execution history of the orchestration instance. At this point, the orchestrator function can be unloaded from memory.

Durable Functions uses Azure Storage as its runtime state store by default, but other storage providers are also supported. This ensures that the execution history of the orchestration instance is always up-to-date.

Cloud orchestration tools can aid in automating disaster recovery processes, ensuring continuous delivery and business continuity in the event of a disaster or outage. This is crucial for maintaining reliability and history.

Orchestrator function code must be deterministic to ensure that the replay pattern works correctly and reliably. Non-deterministic code may result in runtime errors or other unexpected behavior.

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The Durable Task Framework keeps track of the history of each function orchestration, which grows continuously as long as the orchestrator function continues to schedule new work. This history is stored using an "event sourcing" technique, meaning that it is possible to get a very detailed log of exactly what happened.

The history includes the input and output data of the orchestrator, as well as the input and output data of every single activity function or sub-orchestrator that was called along the way. You can access the status of an orchestrator by calling the Get Instance Status API or using DurableOrchestrationClient.GetStatusAsync.

The history table contains several columns, including PartitionKey, EventType, Timestamp, Input, Name, Result, and Status. The PartitionKey contains the instance ID of the orchestration, and the EventType represents the type of the event.

Here's a breakdown of the history table columns:

The history of each orchestration is stored in a table in Azure Table Storage, which can grow critically large if the orchestrator function goes into an infinite loop and continuously schedules work.

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Durable timers can schedule delays or timeout handling on async actions, a crucial aspect of ensuring reliability in cloud orchestration.

Orchestrations can use durable timers instead of language-native "sleep" APIs, which can be less reliable and more prone to errors.

Durable timers are a key feature in orchestrator functions, allowing you to set up delays or timeouts with ease.

For more information on implementing durable timers, see the Durable timers article for examples and detailed guidance.

Durable timers can be used in combination with other features like activity functions, sub-orchestrations, and entity functions to create robust and reliable orchestrations.

To ensure deterministic behavior, it's essential to follow the code constraints topic, which outlines the requirements for writing orchestrator function code.

By using durable timers and following the determinism requirements, you can create orchestrations that are reliable, efficient, and easy to maintain.