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في هذا الدرس

make services start in a usable order.

الموضوعات المخطط لها

• depends_on alone only waits for the container to start, not to be ready.
• A healthcheck runs a command repeatedly to mark a service healthy.
• depends_on: db: condition: service_healthy makes the app wait for a healthy database.
• Postgres check: pg_isready. Tune interval, timeout, retries.
• Apps should still retry connections; startup order is a convenience, not a guarantee.