I'm new to Docker and using it to learn and experiment. I currently have two services sharing a PostgreSQL container, with an initial migration that creates a separate database and user for each service before the applications start.
As I add more services, I want the setup to remain scalable, resource-efficient, secure, and easy to maintain. Should each service have its own database instance, or is it better for several services to share one PostgreSQL instance while using separate databases and users? I'm especially interested in the trade-offs involving resource usage, maintenance, security, and failure isolation.
4 Answers
There isn’t one universal answer. For local development, a single shared database instance is usually the simplest and cheapest option. In production, one instance with a separate database and user per service is often a good compromise. Dedicated instances provide stronger failure and resource isolation, but they cost more and create more operational work. Keep production databases on an internal network rather than exposing their ports publicly.
A separate database per application or service is generally a solid default. Separate users let you grant only the permissions each service needs, and a bad migration or damaged index in one database is less likely to affect the others. Multiple databases inside one PostgreSQL instance add little overhead compared with running several complete database servers.
Think of the choices as separate levels of isolation: shared instance with separate databases, separate database containers on the same host, or completely separate database servers. Start with separate databases and credentials on one instance unless you have a clear need for stronger isolation. Split them into separate instances later when workloads, availability requirements, or security boundaries justify the extra resources.
Running one database container per service is not automatically better. Each database server consumes memory and needs backups, upgrades, monitoring, and recovery procedures. Separate instances make sense when services have very different workloads or one service could exhaust the others’ resources; otherwise, a shared PostgreSQL instance with strict permissions is often more efficient.
The services don’t necessarily need to be full microservices, but keeping their data ownership and responsibilities isolated makes future scaling and maintenance easier.