Docker volume management and data persistence patterns

<p>Docker containers are ephemeral — data stored inside the container is lost on restart. Need to persist PostgreSQL data, handle Redis persistence, and share files between containers. Confusion between named volumes and bind mounts.</p>

<p>Use named volumes for databases (Docker manages location), bind mounts for development code:</p> <div class="highlight"><pre><span></span><code><span class="nt">version</span><span class="p">:</span><span class="w"> </span><span class="s">'3.9'</span> <span class="nt">services</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">image</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">pgvector/pgvector:pg17</span> <span class="w"> </span><span class="nt">volumes</span><span class="p">:</span> <span class="w"> </span><span class="c1"># Named volume — Docker manages the path, persists across container recreates</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">postgres_data:/var/lib/postgresql/data</span> <span class="w"> </span><span class="c1"># Bind mount for init scripts</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">./migrations/init.sql:/docker-entrypoint-initdb.d/init.sql:ro</span> <span class="w"> </span><span class="nt">environment</span><span class="p">:</span> <span class="w"> </span><span class="nt">POSTGRES_DB</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">myapp</span> <span class="w"> </span><span class="nt">POSTGRES_USER</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">myuser</span> <span class="w"> </span><span class="nt">POSTGRES_PASSWORD</span><span class="p">:</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">mypassword</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">volumes</span><span class="p">:</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">redis_data:/data</span> <span class="w"> </span><span class="c1"># Enable AOF persistence</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">redis-server --appendonly yes --appendfsync everysec</span> <span class="w"> </span><span class="nt">api</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">volumes</span><span class="p">:</span> <span class="w"> </span><span class="c1"># Bind mount for hot reload in development</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">./api:/app:cached</span> <span class="w"> </span><span class="c1"># Named volume for compiled .pyc files (faster than bind mount)</span> <span class="w"> </span><span class="p p-Indicator">-</span><span class="w"> </span><span class="l l-Scalar l-Scalar-Plain">api_pycache:/app/__pycache__</span> <span class="nt">volumes</span><span class="p">:</span> <span class="w"> </span><span class="nt">postgres_data</span><span class="p">:</span> <span class="w"> </span><span class="c1"># Optional: use external volume managed outside compose</span> <span class="w"> </span><span class="c1"># external: true</span> <span class="w"> </span><span class="nt">redis_data</span><span class="p">:</span> <span class="w"> </span><span class="nt">api_pycache</span><span class="p">:</span> </code></pre></div> <div class="highlight"><pre><span></span><code><span class="c1"># List volumes</span> docker<span class="w"> </span>volume<span class="w"> </span>ls <span class="c1"># Inspect volume location</span> docker<span class="w"> </span>volume<span class="w"> </span>inspect<span class="w"> </span>myapp_postgres_data <span class="c1"># Remove volumes on teardown (destructive!)</span> docker-compose<span class="w"> </span>down<span class="w"> </span>-v <span class="c1"># Backup named volume</span> docker<span class="w"> </span>run<span class="w"> </span>--rm<span class="w"> </span>-v<span class="w"> </span>myapp_postgres_data:/data<span class="w"> </span>-v<span class="w"> </span><span class="k">$(</span><span class="nb">pwd</span><span class="k">)</span>:/backup<span class="w"> </span><span class="se">\</span> <span class="w"> </span>alpine<span class="w"> </span>tar<span class="w"> </span>czf<span class="w"> </span>/backup/postgres_backup.tar.gz<span class="w"> </span>/data </code></pre></div> <p>Named volumes survive <code>docker-compose down</code> but NOT <code>docker-compose down -v</code>. Bind mounts reflect host changes immediately — ideal for dev. Always use named volumes in production.</p>