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| </style> |
| <script src="/js/darkmode-docs.js"></script><link rel="canonical" href="https://stormcrawler.apache.org/docs/latest/extending.html"></head> |
| <body class="article"> |
| <div id="header"> |
| <div id="toc" class="toc"> |
| <div id="toctitle">Table of Contents</div> |
| <ul class="sectlevel1"> |
| <li><a href="#_extending_and_operating_stormcrawler">Extending and Operating StormCrawler</a> |
| <ul class="sectlevel2"> |
| <li><a href="#_writing_custom_components">Writing Custom Components</a></li> |
| <li><a href="#_politeness_and_rate_limiting">Politeness and Rate Limiting</a></li> |
| <li><a href="#_error_handling_and_retry_logic">Error Handling and Retry Logic</a></li> |
| <li><a href="#_monitoring_and_metrics">Monitoring and Metrics</a></li> |
| <li><a href="#_scaling_and_tuning">Scaling and Tuning</a></li> |
| <li><a href="#_security_considerations">Security Considerations</a></li> |
| </ul> |
| </li> |
| </ul> |
| </div> |
| </div> |
| <div id="content"> |
| <div class="sect1"> |
| <h2 id="_extending_and_operating_stormcrawler">Extending and Operating StormCrawler</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>This section provides practical guides for extending StormCrawler with custom components, tuning crawl performance, and operating crawlers in production.</p> |
| </div> |
| <div class="sect2"> |
| <h3 id="_writing_custom_components">Writing Custom Components</h3> |
| <div class="sect3"> |
| <h4 id="_custom_url_filter">Custom URL Filter</h4> |
| <div class="paragraph"> |
| <p>URL filters accept, reject, or modify URLs during parsing and redirection handling. To create a custom filter, extend the abstract <code>URLFilter</code> class and implement the <code>filter</code> method.</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="keyword">import</span> <span class="include">org.apache.stormcrawler.filtering.URLFilter</span>; |
| <span class="keyword">import</span> <span class="include">org.apache.stormcrawler.Metadata</span>; |
| <span class="keyword">import</span> <span class="include">com.fasterxml.jackson.databind.JsonNode</span>; |
| <span class="keyword">import</span> <span class="include">java.net.URL</span>; |
| <span class="keyword">import</span> <span class="include">java.util.Map</span>; |
| |
| <span class="directive">public</span> <span class="type">class</span> <span class="class">MyURLFilter</span> <span class="directive">extends</span> URLFilter { |
| |
| <span class="directive">private</span> <span class="type">int</span> maxLength; |
| |
| <span class="annotation">@Override</span> |
| <span class="directive">public</span> <span class="type">void</span> configure(<span class="predefined-type">Map</span><<span class="predefined-type">String</span>, <span class="predefined-type">Object</span>> stormConf, JsonNode paramNode) { |
| maxLength = paramNode.path(<span class="string"><span class="delimiter">"</span><span class="content">maxLength</span><span class="delimiter">"</span></span>).asInt(<span class="integer">1024</span>); |
| } |
| |
| <span class="annotation">@Override</span> |
| <span class="directive">public</span> <span class="predefined-type">String</span> filter(<span class="predefined-type">URL</span> sourceUrl, Metadata sourceMetadata, <span class="predefined-type">String</span> urlToFilter) { |
| <span class="keyword">if</span> (urlToFilter.length() > maxLength) { |
| <span class="keyword">return</span> <span class="predefined-constant">null</span>; <span class="comment">// reject</span> |
| } |
| <span class="keyword">return</span> urlToFilter; <span class="comment">// accept (or return a normalized version)</span> |
| } |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Register the filter in <code>urlfilters.json</code>:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="json">{ |
| <span class="key"><span class="delimiter">"</span><span class="content">org.apache.stormcrawler.filtering.URLFilters</span><span class="delimiter">"</span></span>: [ |
| { |
| <span class="key"><span class="delimiter">"</span><span class="content">class</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">com.example.MyURLFilter</span><span class="delimiter">"</span></span>, |
| <span class="key"><span class="delimiter">"</span><span class="content">name</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">MyURLFilter</span><span class="delimiter">"</span></span>, |
| <span class="key"><span class="delimiter">"</span><span class="content">params</span><span class="delimiter">"</span></span>: { |
| <span class="key"><span class="delimiter">"</span><span class="content">maxLength</span><span class="delimiter">"</span></span>: <span class="integer">2048</span> |
| } |
| } |
| ] |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Filters are executed in the order they appear in the JSON file. Return <code>null</code> to reject a URL, or return the (possibly modified) URL string to accept it.</p> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_custom_parse_filter">Custom Parse Filter</h4> |
| <div class="paragraph"> |
| <p>Parse filters extract data from fetched documents and can modify metadata and outlinks. Extend <code>ParseFilter</code> and implement the <code>filter</code> method.</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="keyword">import</span> <span class="include">org.apache.stormcrawler.parse.ParseFilter</span>; |
| <span class="keyword">import</span> <span class="include">org.apache.stormcrawler.parse.ParseResult</span>; |
| <span class="keyword">import</span> <span class="include">com.fasterxml.jackson.databind.JsonNode</span>; |
| <span class="keyword">import</span> <span class="include">org.w3c.dom.DocumentFragment</span>; |
| <span class="keyword">import</span> <span class="include">java.util.Map</span>; |
| |
| <span class="directive">public</span> <span class="type">class</span> <span class="class">MyParseFilter</span> <span class="directive">extends</span> ParseFilter { |
| |
| <span class="directive">private</span> <span class="predefined-type">String</span> metadataKey; |
| |
| <span class="annotation">@Override</span> |
| <span class="directive">public</span> <span class="type">void</span> configure(<span class="predefined-type">Map</span><<span class="predefined-type">String</span>, <span class="predefined-type">Object</span>> stormConf, JsonNode paramNode) { |
| metadataKey = paramNode.path(<span class="string"><span class="delimiter">"</span><span class="content">key</span><span class="delimiter">"</span></span>).asText(<span class="string"><span class="delimiter">"</span><span class="content">custom-field</span><span class="delimiter">"</span></span>); |
| } |
| |
| <span class="annotation">@Override</span> |
| <span class="directive">public</span> <span class="type">boolean</span> needsDOM() { |
| <span class="keyword">return</span> <span class="predefined-constant">false</span>; <span class="comment">// set to true if you need the DOM tree</span> |
| } |
| |
| <span class="annotation">@Override</span> |
| <span class="directive">public</span> <span class="type">void</span> filter(<span class="predefined-type">String</span> url, <span class="type">byte</span><span class="type">[]</span> content, DocumentFragment doc, |
| ParseResult parse) { |
| <span class="comment">// Extract data and store in metadata</span> |
| parse.get(url).getMetadata().setValue(metadataKey, <span class="string"><span class="delimiter">"</span><span class="content">extracted-value</span><span class="delimiter">"</span></span>); |
| } |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Register it in <code>parsefilters.json</code>:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="json">{ |
| <span class="key"><span class="delimiter">"</span><span class="content">org.apache.stormcrawler.parse.ParseFilters</span><span class="delimiter">"</span></span>: [ |
| { |
| <span class="key"><span class="delimiter">"</span><span class="content">class</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">com.example.MyParseFilter</span><span class="delimiter">"</span></span>, |
| <span class="key"><span class="delimiter">"</span><span class="content">name</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">MyParseFilter</span><span class="delimiter">"</span></span>, |
| <span class="key"><span class="delimiter">"</span><span class="content">params</span><span class="delimiter">"</span></span>: { |
| <span class="key"><span class="delimiter">"</span><span class="content">key</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">custom-field</span><span class="delimiter">"</span></span> |
| } |
| } |
| ] |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>If <code>needsDOM()</code> returns <code>false</code> for all configured parse filters, the parsing bolt skips DOM generation entirely, improving performance.</p> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_custom_protocol">Custom Protocol</h4> |
| <div class="paragraph"> |
| <p>Protocol implementations define how content is fetched. Implement the <code>Protocol</code> interface:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="keyword">import</span> <span class="include">org.apache.stormcrawler.protocol.Protocol</span>; |
| <span class="keyword">import</span> <span class="include">org.apache.stormcrawler.protocol.ProtocolResponse</span>; |
| <span class="keyword">import</span> <span class="include">org.apache.stormcrawler.Metadata</span>; |
| <span class="keyword">import</span> <span class="include">crawlercommons.robots.BaseRobotRules</span>; |
| <span class="keyword">import</span> <span class="include">org.apache.storm.Config</span>; |
| |
| <span class="directive">public</span> <span class="type">class</span> <span class="class">MyProtocol</span> <span class="directive">implements</span> Protocol { |
| |
| <span class="annotation">@Override</span> |
| <span class="directive">public</span> <span class="type">void</span> configure(Config conf) { |
| <span class="comment">// Initialize from Storm configuration</span> |
| } |
| |
| <span class="annotation">@Override</span> |
| <span class="directive">public</span> ProtocolResponse getProtocolOutput(<span class="predefined-type">String</span> url, Metadata metadata) |
| <span class="directive">throws</span> <span class="exception">Exception</span> { |
| <span class="type">byte</span><span class="type">[]</span> content = <span class="comment">/* fetch content */</span>; |
| <span class="type">int</span> statusCode = <span class="integer">200</span>; |
| Metadata responseMeta = <span class="keyword">new</span> Metadata(); |
| <span class="keyword">return</span> <span class="keyword">new</span> ProtocolResponse(content, statusCode, responseMeta); |
| } |
| |
| <span class="annotation">@Override</span> |
| <span class="directive">public</span> BaseRobotRules getRobotRules(<span class="predefined-type">String</span> url) { |
| <span class="keyword">return</span> RobotRulesParser.EMPTY_RULES; |
| } |
| |
| <span class="annotation">@Override</span> |
| <span class="directive">public</span> <span class="type">void</span> cleanup() {} |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Register it in your configuration YAML:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="yaml"><span class="key">http.protocol.implementation</span>: <span class="string"><span class="delimiter">"</span><span class="content">com.example.MyProtocol</span><span class="delimiter">"</span></span> |
| <span class="key">https.protocol.implementation</span>: <span class="string"><span class="delimiter">"</span><span class="content">com.example.MyProtocol</span><span class="delimiter">"</span></span></code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Use the <a href="https://github.com/apache/stormcrawler/blob/stormcrawler-3.6.0/core/src/main/java/org/apache/stormcrawler/protocol/DelegatorProtocol.java">DelegatorProtocol</a> when you need to route URLs to different protocol implementations based on metadata or URL patterns.</p> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_custom_page_action_playwright">Custom Page Action (Playwright)</h4> |
| <div class="paragraph"> |
| <p>The <a href="https://github.com/apache/stormcrawler/tree/stormcrawler-3.6.0/external/playwright">Playwright protocol</a> exposes a <code>PageAction</code> extension point so you can plug site-specific post-navigate behaviour (tab/accordion expansion, cookie-banner dismissal, infinite-scroll, custom <code>evaluate()</code> calls, screenshotting, …​) into the protocol without subclassing it. Actions are loaded as an ordered chain from a JSON file referenced by <code>playwright.page.actions.config.file</code> and follow the same <code>Configurable</code> lifecycle as URL/parse filters. The chain runs after <code>page.navigate()</code> succeeds and before <code>page.content()</code> is captured, so any DOM mutations land in the rendered content returned by the protocol.</p> |
| </div> |
| <div class="paragraph"> |
| <p>A handful of built-in actions ship with the module — <code>DismissOverlayAction</code>, <code>ExpandClickablesAction</code>, <code>ScrollToBottomAction</code>, <code>EvaluateAction</code>, <code>WaitForSelectorAction</code>, <code>ScreenshotAction</code>. Reach for a custom action when none of those fit. Extend <code>PageAction</code> and implement <code>apply</code>:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="keyword">import</span> <span class="include">org.apache.stormcrawler.protocol.playwright.PageAction</span>; |
| <span class="keyword">import</span> <span class="include">org.apache.stormcrawler.Metadata</span>; |
| <span class="keyword">import</span> <span class="include">com.fasterxml.jackson.databind.JsonNode</span>; |
| <span class="keyword">import</span> <span class="include">com.microsoft.playwright.Page</span>; |
| <span class="keyword">import</span> <span class="include">java.util.Map</span>; |
| |
| <span class="directive">public</span> <span class="type">class</span> <span class="class">MyPageAction</span> <span class="directive">extends</span> PageAction { |
| |
| <span class="directive">private</span> <span class="predefined-type">String</span> selector; |
| |
| <span class="annotation">@Override</span> |
| <span class="directive">public</span> <span class="type">void</span> configure(<span class="predefined-type">Map</span><<span class="predefined-type">String</span>, <span class="predefined-type">Object</span>> stormConf, JsonNode params) { |
| <span class="keyword">if</span> (!params.has(<span class="string"><span class="delimiter">"</span><span class="content">selector</span><span class="delimiter">"</span></span>)) { |
| <span class="keyword">throw</span> <span class="keyword">new</span> <span class="exception">IllegalArgumentException</span>(<span class="string"><span class="delimiter">"</span><span class="content">MyPageAction requires 'selector'</span><span class="delimiter">"</span></span>); |
| } |
| <span class="local-variable">this</span>.selector = params.get(<span class="string"><span class="delimiter">"</span><span class="content">selector</span><span class="delimiter">"</span></span>).asText(); |
| } |
| |
| <span class="annotation">@Override</span> |
| <span class="directive">public</span> <span class="type">void</span> apply(Page page, <span class="predefined-type">String</span> url, |
| Metadata sourceMetadata, Metadata responseMetadata) { |
| page.locator(selector).click(); |
| } |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Reference the action by its fully-qualified class name in the chain JSON:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="json">{ |
| <span class="key"><span class="delimiter">"</span><span class="content">org.apache.stormcrawler.protocol.playwright.PageActions</span><span class="delimiter">"</span></span>: [ |
| { |
| <span class="key"><span class="delimiter">"</span><span class="content">class</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">com.example.MyPageAction</span><span class="delimiter">"</span></span>, |
| <span class="key"><span class="delimiter">"</span><span class="content">name</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">my-action</span><span class="delimiter">"</span></span>, |
| <span class="key"><span class="delimiter">"</span><span class="content">params</span><span class="delimiter">"</span></span>: { <span class="key"><span class="delimiter">"</span><span class="content">selector</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">#load-more</span><span class="delimiter">"</span></span> } |
| } |
| ] |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Per-action failures in <code>apply()</code> are logged and swallowed by the chain wrapper so one bad action cannot abort the rest. If you need a hard failure on misconfiguration, throw from <code>configure()</code> — that propagates at topology start-up, before any URL is fetched.</p> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_custom_bolt_or_spout">Custom Bolt or Spout</h4> |
| <div class="paragraph"> |
| <p>For a bolt that emits on the status stream (like fetchers and parsers), extend <a href="https://github.com/apache/stormcrawler/blob/stormcrawler-3.6.0/core/src/main/java/org/apache/stormcrawler/bolt/StatusEmitterBolt.java">StatusEmitterBolt</a>:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="java"><span class="keyword">import</span> <span class="include">org.apache.stormcrawler.bolt.StatusEmitterBolt</span>; |
| <span class="keyword">import</span> <span class="include">org.apache.storm.tuple.Tuple</span>; |
| |
| <span class="directive">public</span> <span class="type">class</span> <span class="class">MyBolt</span> <span class="directive">extends</span> StatusEmitterBolt { |
| |
| <span class="annotation">@Override</span> |
| <span class="directive">public</span> <span class="type">void</span> execute(Tuple tuple) { |
| <span class="predefined-type">String</span> url = tuple.getStringByField(<span class="string"><span class="delimiter">"</span><span class="content">url</span><span class="delimiter">"</span></span>); |
| <span class="type">byte</span><span class="type">[]</span> content = tuple.getBinaryByField(<span class="string"><span class="delimiter">"</span><span class="content">content</span><span class="delimiter">"</span></span>); |
| Metadata metadata = (Metadata) tuple.getValueByField(<span class="string"><span class="delimiter">"</span><span class="content">metadata</span><span class="delimiter">"</span></span>); |
| |
| <span class="comment">// Process content...</span> |
| |
| collector.emit(tuple, <span class="keyword">new</span> Values(url, content, metadata)); |
| collector.ack(tuple); |
| } |
| |
| <span class="annotation">@Override</span> |
| <span class="directive">public</span> <span class="type">void</span> declareOutputFields(OutputFieldsDeclarer declarer) { |
| declarer.declare(<span class="keyword">new</span> Fields(<span class="string"><span class="delimiter">"</span><span class="content">url</span><span class="delimiter">"</span></span>, <span class="string"><span class="delimiter">"</span><span class="content">content</span><span class="delimiter">"</span></span>, <span class="string"><span class="delimiter">"</span><span class="content">metadata</span><span class="delimiter">"</span></span>)); |
| declarer.declareStream( |
| org.apache.stormcrawler.Constants.StatusStreamName, |
| <span class="keyword">new</span> Fields(<span class="string"><span class="delimiter">"</span><span class="content">url</span><span class="delimiter">"</span></span>, <span class="string"><span class="delimiter">"</span><span class="content">metadata</span><span class="delimiter">"</span></span>, <span class="string"><span class="delimiter">"</span><span class="content">status</span><span class="delimiter">"</span></span>)); |
| } |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>For a custom spout, extend <code>BaseRichSpout</code> and implement <code>open()</code>, <code>nextTuple()</code>, <code>ack()</code>, <code>fail()</code>, and <code>declareOutputFields()</code>. See <a href="https://github.com/apache/stormcrawler/blob/stormcrawler-3.6.0/core/src/main/java/org/apache/stormcrawler/spout/FileSpout.java">FileSpout</a> for a simple example. For spouts backed by a storage layer, extend <a href="https://github.com/apache/stormcrawler/blob/stormcrawler-3.6.0/core/src/main/java/org/apache/stormcrawler/persistence/AbstractQueryingSpout.java">AbstractQueryingSpout</a> instead.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_politeness_and_rate_limiting">Politeness and Rate Limiting</h3> |
| <div class="paragraph"> |
| <p>StormCrawler enforces politeness at multiple levels to avoid overloading target servers.</p> |
| </div> |
| <div class="sect3"> |
| <h4 id="_queue_based_politeness">Queue-Based Politeness</h4> |
| <div class="paragraph"> |
| <p>The <strong>FetcherBolt</strong> groups incoming URLs into queues based on the <code>fetcher.queue.mode</code> setting:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><code>byHost</code> (default) — one queue per hostname</p> |
| </li> |
| <li> |
| <p><code>byDomain</code> — one queue per registered domain (e.g., <code>sub.example.com</code> and <code>example.com</code> share a queue)</p> |
| </li> |
| <li> |
| <p><code>byIP</code> — one queue per resolved IP address</p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>Each queue enforces a minimum delay between consecutive requests. The delay is determined by:</p> |
| </div> |
| <div class="olist arabic"> |
| <ol class="arabic"> |
| <li> |
| <p>The <code>Crawl-delay</code> directive in the site’s <code>robots.txt</code> (if present and within limits)</p> |
| </li> |
| <li> |
| <p>The <code>fetcher.server.delay</code> default (1 second)</p> |
| </li> |
| <li> |
| <p>For multi-threaded queues, <code>fetcher.server.min.delay</code> is used instead</p> |
| </li> |
| </ol> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_crawl_delay_handling">Crawl-Delay Handling</h4> |
| <div class="paragraph"> |
| <p>When <code>robots.txt</code> specifies a <code>Crawl-delay</code>:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>If the delay is <strong>smaller</strong> than <code>fetcher.server.delay</code> and <code>fetcher.server.delay.force</code> is <code>true</code>, the larger default delay is used instead</p> |
| </li> |
| <li> |
| <p>If the delay is <strong>larger</strong> than <code>fetcher.max.crawl.delay</code>:</p> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><code>fetcher.max.crawl.delay.force: false</code> (default) — the queue is skipped and the URL gets an ERROR status</p> |
| </li> |
| <li> |
| <p><code>fetcher.max.crawl.delay.force: true</code> — the delay is capped at <code>fetcher.max.crawl.delay</code></p> |
| </li> |
| </ul> |
| </div> |
| </li> |
| </ul> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_robots_txt_compliance">Robots.txt Compliance</h4> |
| <div class="paragraph"> |
| <p>StormCrawler fetches and caches <code>robots.txt</code> rules per host. The cache is configured via:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><code>robots.cache.spec</code> — Guava cache spec for valid rules (default: 6 hour expiry, 10000 entries)</p> |
| </li> |
| <li> |
| <p><code>robots.error.cache.spec</code> — cache spec for error responses (default: 1 hour expiry)</p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>Individual aspects of robot compliance can be toggled:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><code>http.robots.file.skip</code> — ignore <code>robots.txt</code> entirely</p> |
| </li> |
| <li> |
| <p><code>http.robots.headers.skip</code> — ignore <code>X-Robots-Tag</code> HTTP headers</p> |
| </li> |
| <li> |
| <p><code>http.robots.meta.skip</code> — ignore <code><meta name="robots"></code> HTML tags</p> |
| </li> |
| <li> |
| <p><code>robots.noFollow.strict</code> — if <code>true</code>, remove all outlinks from pages marked as <code>noFollow</code></p> |
| </li> |
| </ul> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_error_handling_and_retry_logic">Error Handling and Retry Logic</h3> |
| <div class="paragraph"> |
| <p>StormCrawler uses a status-based system to handle errors and schedule retries.</p> |
| </div> |
| <div class="sect3"> |
| <h4 id="_status_lifecycle">Status Lifecycle</h4> |
| <div class="paragraph"> |
| <p>Each URL has a <code>Status</code> value that drives scheduling:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><strong>DISCOVERED</strong> — new URL, not yet fetched</p> |
| </li> |
| <li> |
| <p><strong>FETCHED</strong> — successfully retrieved and processed</p> |
| </li> |
| <li> |
| <p><strong>FETCH_ERROR</strong> — transient error (network timeout, HTTP 5xx). Will be retried.</p> |
| </li> |
| <li> |
| <p><strong>ERROR</strong> — terminal error (too many retries, HTTP 4xx). Not retried by default.</p> |
| </li> |
| <li> |
| <p><strong>REDIRECTION</strong> — HTTP 3xx redirect encountered</p> |
| </li> |
| </ul> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_retry_mechanism">Retry Mechanism</h4> |
| <div class="paragraph"> |
| <p>When a URL receives <code>FETCH_ERROR</code> status, the <code>AbstractStatusUpdaterBolt</code> increments a <code>fetch.error.count</code> counter in the URL’s metadata. Once this counter reaches <code>max.fetch.errors</code> (default: 3), the status is escalated to <code>ERROR</code>.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The <code>DefaultScheduler</code> computes the next fetch date based on status:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><strong>FETCHED</strong> — <code>fetchInterval.default</code> (default: 1440 minutes = 1 day)</p> |
| </li> |
| <li> |
| <p><strong>FETCH_ERROR</strong> — <code>fetchInterval.fetch.error</code> (default: 120 minutes = 2 hours)</p> |
| </li> |
| <li> |
| <p><strong>ERROR</strong> — <code>fetchInterval.error</code> (default: -1 = never refetch)</p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>On a successful fetch, the error counter and error metadata (<code>error.cause</code>, <code>error.message</code>, <code>error.source</code>) are cleared automatically.</p> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_custom_fetch_intervals">Custom Fetch Intervals</h4> |
| <div class="paragraph"> |
| <p>You can set fetch intervals based on metadata key-value pairs:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="yaml"><span class="comment"># All feeds refetch every 10 minutes</span> |
| <span class="error">fetchInterval.isFeed=true</span>: <span class="error">10</span> |
| |
| <span class="comment"># Feeds with fetch errors retry after 60 minutes</span> |
| <span class="error">fetchInterval.FETCH_ERROR.isFeed=true</span>: <span class="error">60</span></code></pre> |
| </div> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_monitoring_and_metrics">Monitoring and Metrics</h3> |
| <div class="paragraph"> |
| <p>StormCrawler exposes metrics through Apache Storm’s built-in metrics system. Bolts register counters, gauges, and averages which are reported at configurable intervals.</p> |
| </div> |
| <div class="sect3"> |
| <h4 id="_key_fetcher_metrics">Key Fetcher Metrics</h4> |
| <div class="paragraph"> |
| <p>The <code>FetcherBolt</code> tracks:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><code>fetcher_counter</code> — event counts (fetched, error, redirection, robots_rules_fetches)</p> |
| </li> |
| <li> |
| <p><code>fetcher_average</code> — averaged values (download_time, queue_wait_time)</p> |
| </li> |
| <li> |
| <p><code>fetcher_average_persec</code> — throughput rates (fetched_per_sec, error_per_sec)</p> |
| </li> |
| <li> |
| <p><code>activethreads</code> — number of currently active fetching threads</p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>The reporting interval is controlled by <code>fetcher.metrics.time.bucket.secs</code> (default: 10 seconds).</p> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_metrics_consumers">Metrics Consumers</h4> |
| <div class="paragraph"> |
| <p>To persist metrics, register a <code>MetricsConsumer</code> in your topology configuration:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="yaml"><span class="key">topology.metrics.consumer.register</span>: |
| - <span class="string"><span class="content">class: "org.apache.stormcrawler.opensearch.metrics.MetricsConsumer"</span></span> |
| <span class="key">parallelism.hint</span>: <span class="string"><span class="content">1</span></span></code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>StormCrawler provides MetricsConsumer implementations for <a href="https://github.com/apache/stormcrawler/tree/stormcrawler-3.6.0/external/opensearch">OpenSearch</a>, <a href="https://github.com/apache/stormcrawler/tree/stormcrawler-3.6.0/external/solr">Solr</a>, and <a href="https://github.com/apache/stormcrawler/tree/stormcrawler-3.6.0/external/sql">SQL</a>.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The <strong>Storm UI</strong> (default port 8080) provides real-time visibility into topology health, including execute/process latency, emit counts, and error rates per bolt and spout.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_scaling_and_tuning">Scaling and Tuning</h3> |
| <div class="sect3"> |
| <h4 id="_thread_and_parallelism_tuning">Thread and Parallelism Tuning</h4> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><code>fetcher.threads.number</code> — total fetching threads across all queues (default: 10). Increase for broader crawls.</p> |
| </li> |
| <li> |
| <p><code>fetcher.threads.per.queue</code> — threads per host/domain/IP queue (default: 1). Increase only for sites that allow aggressive crawling.</p> |
| </li> |
| <li> |
| <p><code>fetcher.maxThreads.host/domain/ip</code> — override threads for a specific queue.</p> |
| </li> |
| <li> |
| <p><code>protocol.instances.num</code> — number of protocol instances (default: 1). Increase for OkHttp connection pool efficiency.</p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>In Flux or topology code, set <code>parallelism</code> for each bolt to control Storm executor allocation. Increase spout parallelism when the frontier is the bottleneck.</p> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_queue_and_buffer_tuning">Queue and Buffer Tuning</h4> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><code>fetcher.max.urls.in.queues</code> — caps total queued URLs to prevent memory exhaustion. -1 for unlimited.</p> |
| </li> |
| <li> |
| <p><code>fetcher.max.queue.size</code> — caps individual queue length.</p> |
| </li> |
| <li> |
| <p><code>urlbuffer.class</code> — URL buffer implementation used by spouts. The default <code>SimpleURLBuffer</code> is suitable for most use cases.</p> |
| </li> |
| </ul> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_memory_and_connection_pooling_okhttp">Memory and Connection Pooling (OkHttp)</h4> |
| <div class="paragraph"> |
| <p>For crawls with many concurrent hosts, tune OkHttp’s connection pool:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="yaml"><span class="key">okhttp.protocol.connection.pool</span>: |
| <span class="key">max.idle.connections</span>: <span class="string"><span class="content">5</span></span> |
| <span class="key">connection.keep.alive</span>: <span class="string"><span class="content">300</span></span></code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Keep the pool size (idle + active) under 1000. For large crawls, increase <code>protocol.instances.num</code> to distribute connections across multiple pools.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect2"> |
| <h3 id="_security_considerations">Security Considerations</h3> |
| <div class="sect3"> |
| <h4 id="_ssltls">SSL/TLS</h4> |
| <div class="paragraph"> |
| <p>By default, StormCrawler’s OkHttp protocol trusts all certificates (<code>http.trust.everything: true</code>). For production crawls over untrusted networks, consider setting this to <code>false</code> and configuring a proper trust store.</p> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_authentication">Authentication</h4> |
| <div class="paragraph"> |
| <p><strong>Basic Authentication</strong> is supported via:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="yaml"><span class="key">http.basicauth.user</span>: <span class="string"><span class="delimiter">"</span><span class="content">username</span><span class="delimiter">"</span></span> |
| <span class="key">http.basicauth.password</span>: <span class="string"><span class="delimiter">"</span><span class="content">password</span><span class="delimiter">"</span></span></code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>These credentials are sent as an <code>Authorization</code> header with every request. For per-site authentication, use metadata-driven headers instead (see <a href="#Metadata-dependent Behavior For HTTP Protocols">[Metadata-dependent Behavior For HTTP Protocols]</a> in the Internals section).</p> |
| </div> |
| </div> |
| <div class="sect3"> |
| <h4 id="_proxy_authentication">Proxy Authentication</h4> |
| <div class="paragraph"> |
| <p>Proxy credentials can be configured via:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="CodeRay highlight"><code data-lang="yaml"><span class="key">http.proxy.host</span>: <span class="string"><span class="delimiter">"</span><span class="content">proxy.example.com</span><span class="delimiter">"</span></span> |
| <span class="key">http.proxy.port</span>: <span class="string"><span class="content">8080</span></span> |
| <span class="key">http.proxy.user</span>: <span class="string"><span class="delimiter">"</span><span class="content">proxyuser</span><span class="delimiter">"</span></span> |
| <span class="key">http.proxy.pass</span>: <span class="string"><span class="delimiter">"</span><span class="content">proxypass</span><span class="delimiter">"</span></span></code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>For rotating proxies, use the <code>MultiProxyManager</code> with a proxy list file. See the <a href="configuration.html">Proxy configuration section</a> for details.</p> |
| </div> |
| </div> |
| </div> |
| </div> |
| </div> |
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