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Clarify the horizontal scaling documentation
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,115 @@ | ||
| <h4 id="scaling_intro"> | ||
| Introduction | ||
| <a class="headerlink" href="#scaling_intro" title="Permalink to this headline">¶</a> | ||
| </h4> | ||
| <p> | ||
| The print has a state containing the job queue and each job's state. To enable horizontal scaling, these | ||
| states must be persisted. | ||
| </p> | ||
| <h4 id="scaling_solus"> | ||
| Solution | ||
| <a class="headerlink" href="#scaling_solus" title="Permalink to this headline">¶</a> | ||
| </h4> | ||
| <p> | ||
| To store the state we use a PostgreSQL database, the database connection should be configured with the | ||
| following Java system properties: | ||
| </p> | ||
|
|
||
| <ul> | ||
| <li><code>db.host</code>: The database server host name</li> | ||
| <li><code>db.port</code>: The database server port (defaults to <code>5432</code>)</li> | ||
| <li><code>db.username</code>: The username to connect to the database</li> | ||
| <li><code>db.password</code>: The password to connect to the database</li> | ||
| <li><code>db.name</code>: The name of the database</li> | ||
| <li><code>db.schema</code>: The schema to use (defaults to <code>public</code>)</li> | ||
| </ul> | ||
|
|
||
| <p> | ||
| The schema should exist, and the necessary tables are created automatically (<code>print_accountings</code>, | ||
| <code>print_job_results</code>, <code>print_job_statuses</code>). In this mode, the container will wait for | ||
| the database to be reachable before actually starting the tomcat server. | ||
| </p> | ||
|
|
||
| <p>The DB polling can be tuned with these two environment variables:</p> | ||
| <ul> | ||
| <li> | ||
| <code>PRINT_CANCEL_OLD_POLL_INTERVAL</code>: How often in seconds the DB is polled for jobs to be canceled | ||
| (default=<code>60</code>s) | ||
| </li> | ||
|
|
||
| <li> | ||
| <code>PRINT_POLL_INTERVAL</code>: How often in seconds the DB is polled for new jobs | ||
| (default=<code>0.5</code>s) | ||
| </li> | ||
| </ul> | ||
|
|
||
| <h5 id="scaling_docker"> | ||
| Docker | ||
| <a class="headerlink" href="#scaling_docker" title="Permalink to this headline">¶</a> | ||
| </h5> | ||
| <p> | ||
| In a Docker environment, the system properties should be added in the <code>CATALINA_OPTS</code> environment | ||
| variable Like that: <code>-D<property name>=<property value></code>. | ||
| </p> | ||
|
|
||
| <h5 id="scaling_kubernetes"> | ||
| Kubernetes | ||
| <a class="headerlink" href="#scaling_kubernetes" title="Permalink to this headline">¶</a> | ||
| </h5> | ||
| <p>In Kubernetes, you can reuse an environment variable with:</p> | ||
| <pre><code> | ||
| env: | ||
| - name: PROPERTY_VALUE | ||
| value: test | ||
| - name: CATALINA_OPTS | ||
| value: -D<property name>==$(PROPERTY_VALUE) | ||
| </code></pre> | ||
|
|
||
| <p>The order is important.</p> | ||
|
|
||
| <p>Full example where we get the database credentials from a secret:</p> | ||
|
|
||
| <pre> | ||
| <code> | ||
| env: | ||
| - name: PGHOST | ||
| valueFrom: | ||
| secretKeyRef: | ||
| key: hostname | ||
| name: database-credential-secret | ||
| - name: PGPORT | ||
| valueFrom: | ||
| secretKeyRef: | ||
| key: port | ||
| name: database-credential-secret | ||
| - name: PGUSER | ||
| valueFrom: | ||
| secretKeyRef: | ||
| key: username | ||
| name: database-credential-secret | ||
| - name: PGPASSWORD | ||
| valueFrom: | ||
| secretKeyRef: | ||
| key: password | ||
| name: database-credential-secret | ||
| - name: PGDATABASE | ||
| valueFrom: | ||
| secretKeyRef: | ||
| key: database | ||
| name: database-credential-secret | ||
| - name: PGSCHEMA | ||
| value: print | ||
| - name: PGOPTIONS | ||
| value: '-c statement_timeout=30000' | ||
| - name: PRINT_POLL_INTERVAL | ||
| value: '1' | ||
| - name: CATALINA_OPTS | ||
| value: >- | ||
| -Ddb.host=$(PGHOST) | ||
| -Ddb.port=$(PGPORT) | ||
| -Ddb.username=$(PGUSER) | ||
| -Ddb.password=$(PGPASSWORD) | ||
| -Ddb.name=$(PGDATABASE) | ||
| -Ddb.schema=$(PGSCHEMA) | ||
| </code> | ||
| </pre> |