103 lines
4.4 KiB
Markdown
103 lines
4.4 KiB
Markdown
---
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id: gce-extensions
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title: "GCE Extensions"
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---
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<!--
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~ Licensed to the Apache Software Foundation (ASF) under one
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~ or more contributor license agreements. See the NOTICE file
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~ distributed with this work for additional information
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~ regarding copyright ownership. The ASF licenses this file
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~ to you under the Apache License, Version 2.0 (the
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To use this Apache Druid (incubating) extension, make sure to [include](../../development/extensions.md#loading-extensions) `gce-extensions`.
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At the moment, this extension enables only Druid to autoscale instances in GCE.
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The extension manages the instances to be scaled up and down through the use of the [Managed Instance Groups](https://cloud.google.com/compute/docs/instance-groups/creating-groups-of-managed-instances#resize_managed_group)
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of GCE (MIG from now on). This choice has been made to ease the configuration of the machines and simplify their
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management.
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For this reason, in order to use this extension, the user must have created
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1. An instance template with the right machine type and image to bu used to run the MiddleManager
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2. A MIG that has been configured to use the instance template created in the point above
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Moreover, in order to be able to rescale the machines in the MIG, the Overlord must run with a service account
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guaranteeing the following two scopes from the [Compute Engine API](https://developers.google.com/identity/protocols/googlescopes#computev1)
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- `https://www.googleapis.com/auth/cloud-platform`
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- `https://www.googleapis.com/auth/compute`
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## Overlord Dynamic Configuration
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The Overlord can dynamically change worker behavior.
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The JSON object can be submitted to the Overlord via a POST request at:
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```
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http://<OVERLORD_IP>:<port>/druid/indexer/v1/worker
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```
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Optional Header Parameters for auditing the config change can also be specified.
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|Header Param Name| Description | Default |
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|----------|-------------|---------|
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|`X-Druid-Author`| author making the config change|""|
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|`X-Druid-Comment`| comment describing the change being done|""|
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A sample worker config spec is shown below:
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```json
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{
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"autoScaler": {
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"envConfig" : {
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"numInstances" : 1,
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"projectId" : "super-project",
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"zoneName" : "us-central-1",
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"managedInstanceGroupName" : "druid-middlemanagers"
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},
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"maxNumWorkers" : 4,
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"minNumWorkers" : 2,
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"type" : "gce"
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}
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}
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```
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The configuration of the autoscaler is quite simple and it is made of two levels only.
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The external level specifies the `type`—always `gce` in this case— and two numeric values,
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the `maxNumWorkers` and `minNumWorkers` used to define the boundaries in between which the
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number of instances must be at any time.
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The internal level is the `envConfig` and it is used to specify
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- The `numInstances` used to specify how many workers will be spawned at each
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request to provision more workers. This is safe to be left to `1`
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- The `projectId` used to specify the name of the project in which the MIG resides
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- The `zoneName` used to identify in which zone of the worlds the MIG is
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- The `managedInstanceGroupName` used to specify the MIG containing the instances created or
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removed
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Please refer to the Overlord Dynamic Configuration section in the main [documentation](../../configuration/index.md)
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for parameters other than the ones specified here, such as `selectStrategy` etc.
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## Known limitations
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- The module internally uses the [ListManagedInstances](https://cloud.google.com/compute/docs/reference/rest/v1/instanceGroupManagers/listManagedInstances)
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call from the API and, while the documentation of the API states that the call can be paged through using the
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`pageToken` argument, the responses to such call do not provide any `nextPageToken` to set such parameter. This means
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that the extension can operate safely with a maximum of 500 MiddleManagers instances at any time (the maximum number
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of instances to be returned for each call).
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