Deploy Amazon IoT Greengrass components to devices
You can deploy components to individual devices or groups of devices with Amazon IoT Greengrass. With deployments, you define the Amazon IoT Greengrass components and configurations to deploy to core devices. Amazon IoT Greengrass deploys to target devices, which are Amazon IoT things or thing groups that represent Greengrass core devices. Amazon IoT Greengrass uses Amazon IoT Core jobs to deploy to your core devices, so you can configure how the job rolls out to your devices.
Each core device runs the combination of the software from the deployments that target the
device. However, deployments to the same target overwrite previous deployments to that target.
When you create a deployment, you define the components and configurations to apply to the core
devices' existing software. When you revise a deployment for a target, you replace the
components from the previous revision with the components in the new revision. For example, you
deploy components A and B to a thing group X. You then
deploy components B and C to a different thing group Y.
As a result, the components A, B, and C all run on any
core device that is a member of both groups. Then, you create another deployment to thing group
X that specifies only component B. As a result, the core devices in
that group no longer run component A.
When a core device receives a deployment, it checks whether the deployment's components are
compatible with the core device. The core device checks whether it meets each component's
platform requirements. The deployment fails if a component doesn't support the core device's
platform. The core device also checks whether each component's dependencies are compatible with
version constraints from other deployments to different targets that include this core device.
For example, you deploy component A to a thing group X, and component
A depends on component com.example.PythonRuntime versions
3.5 - 3.10. You then deploy component B to a thing group
Y, and component B depends on component
com.example.PythonRuntime versions 3.7 - 3.10. As a
result, core devices in these thing groups determine that they can deploy versions
3.7 - 3.10 of the com.example.PythonRuntime component,
because these versions are where the deployments' version constraints overlap. Then, you deploy
component C to a thing group Z, and component C depends
on component com.example.PythonRuntime versions 2.6 - 2.7.
This deployment fails, because there's no component version that meets the version constraints
2.6 - 2.7 and 3.7 - 3.10. Amazon IoT Greengrass uses NPM semantic version constraints
Before a core device applies a deployment, it notifies each component on the core device by default. Greengrass components can respond to these notifications to defer the deployment. You might want to defer a deployment when the device has a low battery level or is running a process that can't be interrupted, for example. For more information, see Tutorial: Develop a Greengrass component that defers component updates. When you create a deployment, you can configure it to apply the deployment without notifying components.
When you remove a core device from a thing group, the component deployment behavior depends on the version of the Greengrass nucleus that the core device runs.
Deployments are continuous. When you create a deployment, Amazon IoT Greengrass rolls out the deployment to target devices that are online. If a target device isn't online, then it receives the deployment the next time it connects to Amazon IoT Greengrass. When you add a core device to a target thing group, Amazon IoT Greengrass sends the device the latest deployment for that thing group.
Each target thing or thing group can have one deployment at a time. This means that when you create a deployment for a target, Amazon IoT Greengrass no longer deploys the previous revision of that target's deployment.
Deployments provide several options that let you control which devices receive an update and how the update deploys. When you create a deployment, you can configure the following options:
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Amazon IoT Greengrass components
Define the components to install and run on the target devices. Amazon IoT Greengrass components are software modules that you deploy and run on Greengrass core devices. Devices receive components only if the component supports the device's platform. This lets you deploy to groups of devices even if the target devices run on multiple platforms. If a component doesn't support the device's platform, the component doesn't deploy to the device.
You can deploy custom components and Amazon-provided components to your devices. When you deploy a component, Amazon IoT Greengrass identifies any component dependencies and deploys them too. For more information, see Develop Amazon IoT Greengrass components and Amazon-provided components.
You define the version and configuration update to deploy for each component. The configuration update specifies how to modify the component's existing configuration on the core device, or the component's default configuration if the component doesn't exist on the core device. You can specify which configuration values to reset to default values and the new configuration values to merge onto the core device. When a core device receives deployments for different targets, and each deployment specifies compatible component versions, the core device applies configuration updates in order based on the timestamp of when you create the deployment. For more information, see Update component configurations.
Important When you deploy a component, Amazon IoT Greengrass installs the latest supported versions of all of that component's dependencies. Because of this, new patch versions of Amazon-provided public components might be automatically deployed to your core devices if you add new devices to a thing group, or you update the deployment that targets those devices. Some automatic updates, such as a nucleus update, can cause your devices to restart unexpectedly.
To prevent unintended updates for a component that is running on your device, we recommend that you directly include your preferred version of that component when you create a deployment. For more information about update behavior for Amazon IoT Greengrass Core software, see Update the Amazon IoT Greengrass Core software (OTA).
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Deployment policies
Define when it's safe to deploy a configuration and what to do if the deployment fails. You can specify whether or not to wait for components to report that they can update. You can also specify whether or not to roll back devices to their previous configuration if they apply a deployment that fails.
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Stop configuration
Define when and how to stop a deployment. The deployment stops and fails if the criteria that you define are met. For example, you can configure a deployment to stop if a percentage of devices fail to apply that deployment after a minimum number of devices receive it.
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Rollout configuration
Define the rate at which a deployments rolls out to the target devices. You can configure an exponential rate increase with minimum and maximum rate bounds.
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Timeout configuration
Define the maximum amount of time each device has to apply a deployment. If a device exceeds the duration that you specify, then the device fails to apply the deployment.
Custom components can define artifacts in S3 buckets. When the Amazon IoT Greengrass Core software deploys a component, it downloads the component's artifacts from the Amazon Web Services Cloud. Core device roles don't allow access to S3 buckets by default. To deploy custom components that define artifacts in an S3 bucket, the core device role must grant permissions to download artifacts from that bucket. For more information, see Allow access to S3 buckets for component artifacts.
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