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HDDS-8975. Clarify SCM HA auto-bootstrap doc #5021

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adoroszlai merged 2 commits into from
Jul 5, 2023
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HDDS-8975. Clarify SCM HA auto-bootstrap doc #5021

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HDDS-8975. Clarify SCM HA auto-bootstrap doc
adoroszlai Jul 3, 2023
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adoroszlai Jul 5, 2023
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35 changes: 27 additions & 8 deletions hadoop-hdds/docs/content/feature/SCM-HA.md
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Expand Up @@ -91,28 +91,47 @@ For reliable HA support choose 3 independent nodes to form a quorum.

## Bootstrap

The initialization of the **first** SCM-HA node is the same as a none-HA SCM:
The initialization of the **first** SCM-HA node is the same as a non-HA SCM:

```
bin/ozone scm --init
ozone scm --init
```

Second and third nodes should be *bootstrapped* instead of init. These clusters will join to the configured RAFT quorum. The id of the current server is identified by DNS name or can be set explicitly by `ozone.scm.node.id`. Most of the time you don't need to set it as DNS based id detection can work well.

```
bin/ozone scm --bootstrap
ozone scm --bootstrap
```

Note: both commands perform one-time initialization. SCM still needs to be started by running `ozone scm --daemon start`.

## Auto-bootstrap

In some environment -- such as containerized / K8s environment -- we need to have a common, unified way to initialize SCM HA quorum. As a remained, the standard initialization flow is the following:
In some environments (e.g. Kubernetes) we need to have a common, unified way to initialize SCM HA quorum. As a reminder, the standard initialization flow is the following:

1. On the first, "primordial" node: `ozone scm --init`
2. On second/third nodes: `ozone scm --bootstrap`

1. On the first, "primordial" node, call `scm --init`
2. On second/third nodes call `scm --bootstrap`
This can be improved: primordial SCM can be configured by setting `ozone.scm.primordial.node.id` in the config to one of the nodes.

This can be changed with using `ozone.scm.primordial.node.id`. You can define the primordial node. After setting this node, you should execute **both** `scm --init` and `scm --bootstrap` on **all** nodes.
```XML
<property>
<name>ozone.scm.primordial.node.id</name>
<value>scm1</value>
</property>
```

With this configuration both `scm --init` and `scm --bootstrap` can be safely executed on **all** SCM nodes. Each node will only perform the action applicable to it based on the `ozone.scm.primordial.node.id` and its own node ID.

Note: SCM still needs to be started after the init/bootstrap process.

```
ozone scm --init
ozone scm --bootstrap
ozone scm --daemon start
```

Based on the `ozone.scm.primordial.node.id`, the init process will be ignored on the second/third nodes and bootstrap process will be ignored on all nodes except the primordial one.
For Docker/Kubernetes, use `ozone scm` to start it in the foreground.

## SCM HA Security

Expand Down