Yarn service provides a way of upgrading/downgrading long running applications without shutting down the application to minimize the downtime during this process. This is an experimental feature which is currently not enabled by default.
Upgrading a Yarn Service is a 3 steps (or 2 steps when auto-finalization of upgrade is chosen) process:
Initiate service upgrade.
This step involves providing the service spec of the newer version of the service. Once, the service upgrade is initiated, the state of the service is changed to UPGRADING.
Upgrade component instances.
This step involves triggering upgrade of individual component instance. By providing an API to upgrade at instance level, users can orchestrate upgrade of the entire service in any order which is relevant for the service.
In addition, there are APIs to upgrade multiple instances, all instances of a component, and all instances of multiple components.
Finalize upgrade.
This step involves finalization of upgrade. With an explicit step to finalize the upgrade, users have a chance to cancel current upgrade in progress. When the user chose to cancel, the service will make the best effort to revert to the previous version.
When the upgrade is finalized, the old service definition is overwritten by the new service definition and the service state changes to STABLE.
A service can be auto-finalized when the upgrade is initialized with -autoFinalize option. With auto-finalization, when all the component-instances of the service have been upgraded, finalization will be performed automatically by the service framework.\
Hadoop 3.2.0 onwards canceling upgrade and express upgrade is also supported.
Cancel upgrade.
Before the upgrade of the service is finalized, the user has an option to cancel the upgrade. This step resolves the dependencies between the components and then sequentially rolls back each component which was upgraded.
Express upgrade.
This is a one-step process to upgrade all the components of the service. It involves providing the service spec of the newer version of the service. The service master then performs the following steps automatically:
a. Discovers all the components that require an upgrade.
b. Resolve dependencies between these components.
c. Triggers upgrade of the components sequentially.
This example shows upgrade of sleeper service. Below is the sleeper service definition
{
"name": "sleeper-service",
"components" :
[
{
"name": "sleeper",
"version": "1.0.0",
"number_of_containers": 1,
"launch_command": "sleep 900000",
"resource": {
"cpus": 1,
"memory": "256"
}
}
]
}
Assuming, user launched an instance of sleeper service named as my-sleeper:
{
"components":
[
{
"configuration": {...},
"containers":
[
{
"bare_host": "0.0.0.0",
"component_instance_name": "sleeper-0",
"hostname": "example.local",
"id": "container_1531508836237_0002_01_000002",
"ip": "0.0.0.0",
"launch_time": 1531941023675,
"state": "READY"
},
{
"bare_host": "0.0.0.0",
"component_instance_name": "sleeper-1",
"hostname": "example.local",
"id": "container_1531508836237_0002_01_000003",
"ip": "0.0.0.0",
"launch_time": 1531941024680,
"state": "READY"
}
],
"dependencies": [],
"launch_command": "sleep 900000",
"name": "sleeper",
"number_of_containers": 2,
"quicklinks": [],
"resource": {...},
"restart_policy": "ALWAYS",
"run_privileged_container": false,
"state": "STABLE"
}
],
"configuration": {...},
"id": "application_1531508836237_0002",
"kerberos_principal": {},
"lifetime": -1,
"name": "my-sleeper",
"quicklinks": {},
"state": "STABLE",
"version": "1.0.0"
}
Below is the configuration in yarn-site.xml required for enabling service upgrade.
<property>
<name>yarn.service.upgrade.enabled</name>
<value>true</value>
</property>
User can initiate upgrade using the below command:
yarn app -upgrade ${service_name} -initate ${path_to_new_service_def_file} [-autoFinalize]
e.g. To upgrade my-sleeper to sleep for 1200000 instead of 900000, the user can upgrade the service to version 1.0.1. Below is the service definition for version 1.0.1 of sleeper-service:
{
"components" :
[
{
"name": "sleeper",
"version": "1.0.1",
"number_of_containers": 1,
"launch_command": "sleep 1200000",
"resource": {
"cpus": 1,
"memory": "256"
}
}
]
}
The command below initiates the upgrade to version 1.0.1.
yarn app -upgrade my-sleeper -initiate sleeper_v101.json
User can upgrade a component instance using the below command:
yarn app -upgrade ${service_name} -instances ${comma_separated_list_of_instance_names}
e.g. The command below upgrades sleeper-0 and sleeper-1 instances of my-service:
yarn app -upgrade my-sleeper -instances sleeper-0,sleeper-1
User can upgrade a component, that is, all the instances of a component with one command:
yarn app -upgrade ${service_name} -components ${comma_separated_list_of_component_names}
e.g. The command below upgrades all the instances of sleeper component of my-service:
yarn app -ugrade my-sleeper -components sleeper
User must finalize the upgrade using the below command (since autoFinalize was not specified during initiate):
yarn app -upgrade ${service_name} -finalize
e.g. The command below finalizes the upgrade of my-sleeper:
yarn app -upgrade my-sleeper -finalize