Docker Compose healthchecks for Redis and worker services

<p>I have Redis and a Python background worker in Docker Compose. I need healthchecks so dependent services only start once Redis is ready, and I want the worker to report healthy only when it is actively connected.</p>

<p>Healthchecks for Redis and worker:</p> <div class="highlight"><pre><span></span><code><span class="nt">services</span><span class="p">:</span> <span class="w"> </span><span class="nt">redis</span><span class="p">:</span> <span class="w"> </span><span class="nt">image</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">redis:7-alpine</span> <span class="w"> </span><span class="nt">healthcheck</span><span class="p">:</span> <span class="w"> </span><span class="nt">test</span><span class="p">:</span><span class="w"> </span><span class="p p-Indicator">[</span><span class="s">"CMD"</span><span class="p p-Indicator">,</span><span class="w"> </span><span class="s">"redis-cli"</span><span class="p p-Indicator">,</span><span class="w"> </span><span class="s">"ping"</span><span class="p p-Indicator">]</span> <span class="w"> </span><span class="nt">interval</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">5s</span> <span class="w"> </span><span class="nt">timeout</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">3s</span> <span class="w"> </span><span class="nt">retries</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">5</span> <span class="w"> </span><span class="nt">start_period</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">10s</span> <span class="w"> </span><span class="nt">worker</span><span class="p">:</span> <span class="w"> </span><span class="nt">build</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">./api</span> <span class="w"> </span><span class="nt">command</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">python -m app.worker</span> <span class="w"> </span><span class="nt">depends_on</span><span class="p">:</span> <span class="w"> </span><span class="nt">postgres</span><span class="p">:</span> <span class="w"> </span><span class="nt">condition</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">service_healthy</span> <span class="w"> </span><span class="nt">redis</span><span class="p">:</span> <span class="w"> </span><span class="nt">condition</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">service_healthy</span> <span class="w"> </span><span class="nt">healthcheck</span><span class="p">:</span> <span class="w"> </span><span class="c1"># Check heartbeat file updated within last 60 seconds:</span> <span class="w"> </span><span class="nt">test</span><span class="p">:</span><span class="w"> </span><span class="p p-Indicator">[</span><span class="s">"CMD-SHELL"</span><span class="p p-Indicator">,</span><span class="w"> </span><span class="s">"test</span><span class="nv"> </span><span class="s">-f</span><span class="nv"> </span><span class="s">/tmp/worker-heartbeat</span><span class="nv"> </span><span class="s">&amp;&amp;</span><span class="nv"> </span><span class="s">[</span><span class="nv"> </span><span class="s">$(($(date</span><span class="nv"> </span><span class="s">+%s)</span><span class="nv"> </span><span class="s">-</span><span class="nv"> </span><span class="s">$(stat</span><span class="nv"> </span><span class="s">-c</span><span class="nv"> </span><span class="s">%Y</span><span class="nv"> </span><span class="s">/tmp/worker-heartbeat)))</span><span class="nv"> </span><span class="s">-lt</span><span class="nv"> </span><span class="s">60</span><span class="nv"> </span><span class="s">]"</span><span class="p p-Indicator">]</span> <span class="w"> </span><span class="nt">interval</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">30s</span> <span class="w"> </span><span class="nt">timeout</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">5s</span> <span class="w"> </span><span class="nt">retries</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">3</span> </code></pre></div> <p>Worker heartbeat:</p> <div class="highlight"><pre><span></span><code><span class="kn">from</span><span class="w"> </span><span class="nn">pathlib</span><span class="w"> </span><span class="kn">import</span> <span class="n">Path</span> <span class="n">HEARTBEAT</span> <span class="o">=</span> <span class="n">Path</span><span class="p">(</span><span class="s1">'/tmp/worker-heartbeat'</span><span class="p">)</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">run_worker</span><span class="p">():</span> <span class="k">while</span> <span class="kc">True</span><span class="p">:</span> <span class="k">try</span><span class="p">:</span> <span class="k">await</span> <span class="n">process_batch</span><span class="p">()</span> <span class="k">except</span> <span class="ne">Exception</span><span class="p">:</span> <span class="n">log</span><span class="o">.</span><span class="n">exception</span><span class="p">(</span><span class="s1">'Batch failed'</span><span class="p">)</span> <span class="k">finally</span><span class="p">:</span> <span class="n">HEARTBEAT</span><span class="o">.</span><span class="n">touch</span><span class="p">()</span> <span class="c1"># Docker checks timestamp</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span> </code></pre></div> <p>Key points: - start_period gives service time to initialize before checks begin - redis-cli ping returns PONG on success - Heartbeat file timestamp check is simpler than a health HTTP server - service_healthy in depends_on waits for healthcheck to pass</p>