[GitHub] [ozone] GlenGeng commented on a change in pull request #2050: HDDS-4948. SCM-HA documentation

[GitBox <gi...@apache.org>]

GlenGeng commented on a change in pull request #2050:
URL: https://github.com/apache/ozone/pull/2050#discussion_r595698722



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File path: hadoop-hdds/docs/content/feature/SCM-HA.md
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@@ -0,0 +1,162 @@
+---
+title: "SCM High Availability"
+weight: 1
+menu:
+   main:
+      parent: Features
+summary: HA setup for Storage Container Manager to avoid any single point of failure.
+---
+<!---
+  Licensed to the Apache Software Foundation (ASF) under one or more
+  contributor license agreements.  See the NOTICE file distributed with
+  this work for additional information regarding copyright ownership.
+  The ASF licenses this file to You under the Apache License, Version 2.0
+  (the "License"); you may not use this file except in compliance with
+  the License.  You may obtain a copy of the License at
+
+      http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+-->
+
+Ozone has two leader nodes (*Ozone Manager* for key space management and *Storage Container Management* for block space management) and storage nodes (Datanode). Data is replicated between Datanodes with the help of RAFT consensus algorithm.
+
+<div class="alert alert-warning" role="alert">
+Please note that SCM-HA is not ready for production in secure environments. Security work is in progress and will be finished soon.
+</div>
+
+To avoid any single point of failure the leader nodes also should have a HA setup.
+
+Both Ozone Manager and Storage Container Manager supports HA. In this mode the internal state is replicated via RAFT (with Apache Ratis) 
+
+This document explains the HA setup of Storage Container Manager (SCM), please check [this page]({{< ref "OM-HA" >}}) for HA setup of Ozone Manager (OM). While they can be setup for HA independently, a reliable, full HA setup requires enabling HA for both services. 
+
+## Configuration
+
+HA mode of Storage Container Manager can be enabled with the following settings in `ozone-site.xml`:
+
+```XML
+<property>
+   <name>ozone.scm.ratis.enable</name>
+   <value>true</value>
+</property>
+```
+One Ozone configuration (`ozone-site.xml`) can support multiple SCM HA node set, multiple Ozone clusters. To select between the available SCM nodes a logical name is required for each of the clusters which can be resolved to the IP addresses (and domain names) of the Storage Container Managers.
+
+This logical name is called `serviceId` and can be configured in the `ozone-site.xml`
+
+Most of the time you need to set only the values of your current cluster:
+
+ ```XML
+<property>
+   <name>ozone.scm.service.ids</name>
+   <value>cluster1</value>
+</property>
+```
+
+For each of the defined `serviceId` a logical configuration name should be defined for each of the servers
+
+```XML
+<property>
+   <name>ozone.scm.nodes.cluster1</name>
+   <value>scm1,scm2,scm3</value>
+</property>
+```
+
+The defined prefixes can be used to define the address of each of the SCM services:
+
+```XML
+<property>
+   <name>ozone.scm.address.cluster1.scm1</name>
+   <value>host1</value>
+</property>
+<property>
+   <name>ozone.scm.address.cluster1.scm1</name>
+   <value>host2</value>
+</property>
+<property>
+   <name>ozone.scm.address.cluster1.scm1</name>
+   <value>host3</value>
+</property>
+```

Review comment:
       the primordial node is an optional configuration, which is used in k8s.




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