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| <h1>Recon</h1> |
| |
| <!--- |
| 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 |
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| http://www.apache.org/licenses/LICENSE-2.0 |
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| 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. |
| --> |
| <p>Recon serves as a management and monitoring console for Ozone. It gives a |
| bird’s-eye view of Ozone and helps users troubleshoot any issues by presenting |
| the current state of the cluster through REST based APIs and rich web UI.</p> |
| <h2 id="high-level-design">High Level Design</h2> |
| <p> |
| |
| <img src="ReconHighLevelDesign.png" alt='Recon High Level Design' class="img-responsive" /> |
| <br/></p> |
| <p>On a high level, Recon collects and aggregates metadata from Ozone Manager (OM), |
| Storage Container Manager (SCM) and Datanodes (DN) and acts as a central |
| management and monitoring console. Ozone administrators can use Recon to query |
| the current state of the system without overloading OM or SCM.</p> |
| <p>Recon maintains multiple databases to enable batch processing, faster querying |
| and to persist aggregate information. It maintains a local copy of OM db and |
| SCM db along with a SQL database for persisting aggregate information.</p> |
| <p>Recon also integrates with Prometheus to provide a HTTP endpoint to query Prometheus |
| for Ozone metrics and also to display a few crucial point in time metrics in |
| the web UI.</p> |
| <h2 id="recon-and-ozone-manager">Recon and Ozone Manager</h2> |
| <p> |
| |
| <img src="ReconOmDesign.png" alt='Recon OM Design' class="img-responsive" /> |
| <br/></p> |
| <p>Recon gets a full snapshot of OM rocks db initially from the leader OM’s HTTP |
| endpoint, untars the file and initializes RocksDB for querying locally. The |
| database is kept in sync by periodically requesting delta updates from the leader |
| OM via RPC calls from the last applied sequence id. If for any reason, the delta |
| updates could not be retrieved or applied to the local db, a full snapshot is |
| requested again to keep the local db in sync with OM db. Due to this, Recon can |
| show stale information since the local db will not always be in sync.</p> |
| <p>The db updates retrieved from OM is then converted into a batch of events for |
| further processing by OM db tasks via <a href="#task-framework">Recon Task Framework</a>.</p> |
| <h2 id="recon-and-storage-container-manager">Recon and Storage Container Manager</h2> |
| <p> |
| |
| <img src="ReconScmDesign.png" alt='Recon SCM Design' class="img-responsive" /> |
| <br/></p> |
| <p>Recon also acts as a passive SCM for datanodes. When Recon is configured in the |
| cluster, all the datanodes register with Recon and send heartbeats, container |
| reports, incremental container reports etc. to Recon similar to SCM. Recon uses |
| all the information it gets from datanodes to construct its own copy of SCM rocks db |
| locally. Recon never sends any command to datanodes in response and just acts as |
| a passive SCM for faster lookup of SCM metadata.</p> |
| <h2 id="a-nametask-frameworka-task-framework"><a name="task-framework"></a> Task Framework</h2> |
| <p>Recon has its own Task framework to enable batch processing of data obtained |
| from OM and SCM. A task can listen to and act upon db events such as <code>PUT</code>, <code>DELETE</code>, |
| <code>UPDATE</code>, etc. on either OM db or SCM db. Based on this, a task either implements |
| <code>org.apache.hadoop.ozone.recon.tasks.ReconOmTask</code> or extends |
| <code>org.apache.hadoop.ozone.recon.scm.ReconScmTask</code>.</p> |
| <p>An example <code>ReconOmTask</code> is <code>ContainerKeyMapperTask</code> that persists the container -> key |
| mapping in RocksDB. This is useful to understand which keys were part of the container |
| when the container is reported missing or is in a bad health state. Another example is |
| <code>FileSizeCountTask</code> which keeps track of count of files within a given file size range in |
| a SQL database. These tasks have implementations for two scenarios:</p> |
| <ul> |
| <li>Full snapshot (reprocess())</li> |
| <li>Delta updates (process())</li> |
| </ul> |
| <p>When a full snapshot of OM db is obtained from the leader OM, the reprocess() |
| is called on all the registered OM tasks. On subsequent delta updates, process() |
| is called on these OM tasks.</p> |
| <p>An example <code>ReconScmTask</code> is <code>ContainerHealthTask</code> that runs in configurable |
| intervals to scan the list of all the containers and to persist the state of |
| unhealthy containers (<code>MISSING</code>, <code>MIS_REPLICATED</code>, <code>UNDER_REPLICATED</code>, <code>OVER_REPLICATED</code>) |
| in a SQL table. This information is used to determine if there are any missing |
| containers in the cluster.</p> |
| <h2 id="recon-and-prometheus">Recon and Prometheus</h2> |
| <p>Recon can integrate with any Prometheus instance configured to collected metrics |
| and can display useful information in Recon UI in Datanodes and Pipelines pages. |
| Recon also exposes a proxy endpoint (<a href="../interface/reconapi.html#metrics">/metrics</a>) |
| to query Prometheus. This integration can be enabled by setting this configuration <code>ozone.recon.prometheus.http.endpoint</code> |
| to the Prometheus endpoint like <code>ozone.recon.prometheus.http.endpoint=http://prometheus:9090</code>.</p> |
| <h2 id="api-reference">API Reference</h2> |
| <p><a href="../interface/reconapi.html">Link to complete API Reference</a></p> |
| <h2 id="persisted-state">Persisted state</h2> |
| <ul> |
| <li> |
| <p>A local copy of <a href="../concept/ozonemanager.html#persisted-state">OM database</a></p> |
| </li> |
| <li> |
| <p>A local copy of <a href="../concept/storagecontainermanager.html#persisted-state">SCM database</a></p> |
| </li> |
| <li> |
| <p>The following data is persisted in Recon in the specified RocksDB directory:</p> |
| <ul> |
| <li>ContainerKey table |
| <ul> |
| <li>Stores the mapping (container, key) -> count</li> |
| </ul> |
| </li> |
| <li>ContainerKeyCount table |
| <ul> |
| <li>Stores containerID -> no. of keys count within the container</li> |
| </ul> |
| </li> |
| </ul> |
| </li> |
| <li> |
| <p>The following data is stored in the configured SQL database (default is Derby):</p> |
| <ul> |
| <li>GlobalStats table |
| <ul> |
| <li>A Key -> Value table to store aggregate information like total |
| number of volumes / buckets / keys present in the cluster</li> |
| </ul> |
| </li> |
| <li>FileCountBySize table |
| <ul> |
| <li>Keeps track of the number of files present within a file size range in the cluster</li> |
| </ul> |
| </li> |
| <li>ReconTaskStatus table |
| <ul> |
| <li>Keeps track of the status and last run timestamp of the registered OM and SCM |
| db tasks in the <a href="#task-framework">Recon Task Framework</a></li> |
| </ul> |
| </li> |
| <li>ContainerHistory table |
| <ul> |
| <li>Stores ContainerReplica -> Datanode mapping with last known timestamp. This |
| is used to determine the last known datanodes when a container is reported missing</li> |
| </ul> |
| </li> |
| <li>UnhealthyContainers table |
| <ul> |
| <li>Keeps track of all the Unhealthy Containers (MISSING, UNDER_REPLICATED, |
| OVER_REPLICATED, MIS_REPLICATED) in the cluster at any given time</li> |
| </ul> |
| </li> |
| </ul> |
| </li> |
| </ul> |
| <h2 id="notable-configurations">Notable configurations</h2> |
| <table> |
| <thead> |
| <tr> |
| <th>key</th> |
| <th>default</th> |
| <th><div style="width: 300px;">description</div></th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td>ozone.recon.http-address</td> |
| <td>0.0.0.0:9888</td> |
| <td>The address and the base port where the Recon web UI will listen on.</td> |
| </tr> |
| <tr> |
| <td>ozone.recon.address</td> |
| <td>0.0.0.0:9891</td> |
| <td>RPC address of the Recon.</td> |
| </tr> |
| <tr> |
| <td>ozone.recon.heatmap.provider</td> |
| <td>none</td> |
| <td>HeatMapProvider for Recon.</td> |
| </tr> |
| <tr> |
| <td>ozone.recon.db.dir</td> |
| <td>none</td> |
| <td>Directory where the Recon Server stores its metadata.</td> |
| </tr> |
| <tr> |
| <td>ozone.recon.om.db.dir</td> |
| <td>none</td> |
| <td>Directory where the Recon Server stores its OM snapshot DB.</td> |
| </tr> |
| <tr> |
| <td>ozone.recon.om.snapshot<br>.task.interval.delay</td> |
| <td>10m</td> |
| <td>Interval in MINUTES by Recon to request OM DB Snapshot / delta updates.</td> |
| </tr> |
| <tr> |
| <td>ozone.recon.task<br>.missingcontainer.interval</td> |
| <td>300s</td> |
| <td>Time interval of the periodic check for Unhealthy Containers in the cluster.</td> |
| </tr> |
| <tr> |
| <td>ozone.recon.task<br>.safemode.wait.threshold</td> |
| <td>300s</td> |
| <td>Max time for Recon to wait before it exits out of safe or warmup mode.</td> |
| </tr> |
| <tr> |
| <td>ozone.recon.sql.db.jooq.dialect</td> |
| <td>DERBY</td> |
| <td>Please refer to <a href="https://www.jooq.org/javadoc/latest/org.jooq/org/jooq/SQLDialect.html">SQL Dialect</a> to specify a different dialect.</td> |
| </tr> |
| <tr> |
| <td>ozone.recon.sql.db.jdbc.url</td> |
| <td>jdbc:derby:${ozone.recon.db.dir}<br>/ozone_recon_derby.db</td> |
| <td>Recon SQL database jdbc url.</td> |
| </tr> |
| <tr> |
| <td>ozone.recon.sql.db.username</td> |
| <td>none</td> |
| <td>Recon SQL database username.</td> |
| </tr> |
| <tr> |
| <td>ozone.recon.sql.db.password</td> |
| <td>none</td> |
| <td>Recon SQL database password.</td> |
| </tr> |
| <tr> |
| <td>ozone.recon.sql.db.driver</td> |
| <td>org.apache.derby.jdbc<br>.EmbeddedDriver</td> |
| <td>Recon SQL database jdbc driver.</td> |
| </tr> |
| </tbody> |
| </table> |
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