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33 lines
1.8 KiB
33 lines
1.8 KiB
<h1>Pinging Reliability Tips</h1>
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<p>Sending monitoring signals over the public internet is inherently unreliable.
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HTTP requests can sometimes take excessively long or fail completely
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for a variety of reasons. Here are some general tips to make your monitoring
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code more robust.</p>
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<h2>Specify HTTP Request Timeout</h2>
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<p>Put a time limit on how long each ping is allowed to take. This is especially
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important when sending a "start" signal at the start of a job: you don't want
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a stuck ping to prevent the actual job from running. Another case is a continuously
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running worker process that pings SITE_NAME after each completed item. A stuck
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request could block the whole process. An explicit per-request time limit mitigates
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this problem.</p>
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<p>Specifying the timeout depends on the tool you use. curl, for example, has the
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<code>--max-time</code> (shorthand: <code>-m</code>) parameter:</p>
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<div class="bash highlight"><pre><span></span><code><span class="c1"># Send an HTTP request, 10 second timeout:</span>
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curl -m <span class="m">10</span> PING_URL
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</code></pre></div>
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<h2>Use Retries</h2>
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<p>To minimize the amount of false alerts you get from SITE_NAME, instruct your HTTP
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client to retry failed requests several times.</p>
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<p>Specifying the retry policy depends on the tool you use. curl, for example, has the
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<code>--retry</code> parameter:</p>
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<div class="bash highlight"><pre><span></span><code><span class="c1"># Retry up to 5 times, uses an increasing delay between each retry (1s, 2s, 4s, 8s, ...)</span>
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curl --retry <span class="m">5</span> PING_URL
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</code></pre></div>
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<h2>Handle Exceptions</h2>
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<p>Make sure you know how your HTTP client handles failed requests. For example,
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if you use an HTTP library that raises exceptions, decide if you want to
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catch the exceptions or let them bubble up.</p>
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