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By default, the Tymeslot Docker image ships with PostgreSQL embedded directly in the container. On first start, the entrypoint script initialises a local PostgreSQL cluster, stores its data in the tymeslot_pg named volume, and Tymeslot connects to it over localhost. This is the simplest possible setup and works well for personal deployments and small teams.

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When to use an external database

Consider switching to an external PostgreSQL instance when you need:
  • High availability — managed services (AWS RDS Multi-AZ, Azure Database for PostgreSQL, DigitalOcean Managed Databases) provide automatic failover that the embedded single-node PostgreSQL cannot.
  • Managed backups — cloud providers handle point-in-time recovery and snapshot retention automatically.
  • Existing infrastructure — you already run a shared PostgreSQL cluster and want Tymeslot to use it rather than operating a separate embedded database.
  • Host-path volume compatibility — the embedded PostgreSQL can fail to initialise on Docker Desktop, rootless Docker, or SELinux-enforcing hosts when a bind-mount is used for the data directory. An external database sidesteps this entirely.

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How detection works

Tymeslot decides whether to start the embedded PostgreSQL based on the value of DATABASE_HOST:
DATABASE_HOST valueBehaviour
localhost (default) or 127.0.0.1The container starts and manages embedded PostgreSQL
Any other hostname or IPThe container skips embedded PostgreSQL and connects to the external host
There is no other flag to set — pointing DATABASE_HOST at an external host is sufficient.
Tymeslot does not create the database or user on an external PostgreSQL server. Both must already exist before you start the container. Tymeslot only runs schema migrations (CREATE TABLE, ALTER TABLE) on the database it connects to — it does not issue CREATE DATABASE or CREATE ROLE.

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Required environment variables

Set all five variables when connecting to an external database: 
DATABASE_HOST=your-db-host.example.com
DATABASE_PORT=5432
POSTGRES_DB=tymeslot
POSTGRES_USER=tymeslot_user
POSTGRES_PASSWORD=a-strong-password
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DATABASE_HOST
string
default:"localhost"
Hostname or IP address of the PostgreSQL server. Any value other than localhost or 127.0.0.1 triggers external-database mode.
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DATABASE_PORT
integer
default:"5432"
PostgreSQL port. Change this only if your provider uses a non-standard port.
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POSTGRES_DB
string
default:"tymeslot"
Name of the database Tymeslot will connect to. Must already exist.
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POSTGRES_USER
string
default:"tymeslot"
PostgreSQL username. Must already exist and have full privileges on POSTGRES_DB.
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POSTGRES_PASSWORD
string
required
Password for POSTGRES_USER.

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Preparing the external database

Before starting Tymeslot, connect to your PostgreSQL instance as a superuser and run: 
-- Create the database
CREATE DATABASE tymeslot;

-- Create the user
CREATE USER tymeslot_user WITH PASSWORD 'a-strong-password';

-- Grant all privileges on the database
GRANT ALL PRIVILEGES ON DATABASE tymeslot TO tymeslot_user;

-- PostgreSQL 15+ requires this additional grant
GRANT ALL ON SCHEMA public TO tymeslot_user;
Tymeslot will run all schema migrations automatically on first startup.

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Connection pool tuning

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DATABASE_POOL_SIZE
integer
default:"60"
Number of database connections in the Ecto pool. The runtime default is 60, which supports Tymeslot’s background job concurrency. For external managed databases with tighter connection limits, lower this value and ensure your PostgreSQL max_connections is set above it. A good rule of thumb: max_connections should be at least DATABASE_POOL_SIZE + 10 to leave headroom for administrative connections.
DATABASE_POOL_SIZE=20

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Network and firewall requirements

The Tymeslot container must be able to reach the database host on DATABASE_PORT (default 5432). Common things to check:
  • Security groups / firewall rules — allow inbound TCP on port 5432 from the Tymeslot container’s IP or security group.
  • PostgreSQL pg_hba.conf — ensure a rule allows the Tymeslot user to connect from the container’s IP with password authentication.
  • DNS resolution — the DATABASE_HOST value must resolve from inside the container. Use a private DNS hostname for managed services (e.g. an AWS VPC endpoint) rather than a public hostname when possible.

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Provider examples

After creating an RDS PostgreSQL instance (version 14 or later), create the database and user as shown above, then set:
DATABASE_HOST=myinstance.xxxxxxxxxxxx.us-east-1.rds.amazonaws.com
DATABASE_PORT=5432
POSTGRES_DB=tymeslot
POSTGRES_USER=tymeslot_user
POSTGRES_PASSWORD=your-rds-password
Make sure the RDS security group allows inbound traffic on port 5432 from your Tymeslot host’s security group or IP address.
RDS enforces SSL for connections by default on recent engine versions. Tymeslot’s Ecto adapter negotiates SSL automatically when the server requests it.

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Disabling the embedded PostgreSQL

When DATABASE_HOST points to an external server, the container entrypoint automatically skips initialising and starting the internal PostgreSQL process. The tymeslot_pg volume is no longer needed and can be left detached or removed. You only need the tymeslot_data volume for uploaded files and application data: 
docker run -d \
  --name tymeslot \
  -p 4000:4000 \
  -e DATABASE_HOST=your-db-host.example.com \
  -e DATABASE_PORT=5432 \
  -e POSTGRES_DB=tymeslot \
  -e POSTGRES_USER=tymeslot_user \
  -e POSTGRES_PASSWORD=your-password \
  -e SECRET_KEY_BASE="$(openssl rand -base64 64 | tr -d '\n')" \
  -e PHX_HOST=tymeslot.yourdomain.com \
  -v tymeslot_data:/app/data \
  luka1thb/tymeslot:latest

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