Mattermost Self‑Hosted Architecture: Minimal Viable Design and Operational Boundaries

Requirements

Define the minimum user load, expected message rate, and compliance needs before choosing a deployment size.

Smallest Suitable Design

# docker-compose.yml snippet
version: '3.8'
services:
  mattermost:
    image: mattermost/mattermost-enterprise-edition:latest
    environment:
      - MM_SQLSETTINGS_DATASOURCE=postgres://:@:5432/mattermost?sslmode=disable&connect_timeout=10
      - MM_FILESETTINGS_DRIVER_NAME=amazons3
      - MM_FILESETTINGS_AMAZONS3BUCKET=
      - MM_FILESETTINGS_AMAZONS3REGION=
      - MM_FILESETTINGS_AMAZONS3ENDPOINT=
      - MM_FILESETTINGS_AMAZONS3ACCESSKEYID=
      - MM_FILESETTINGS_AMAZONS3SECRETACCESSKEY=
    ports:
      - '8065:8065'
  postgres:
    image: postgres:15-alpine
    environment:
      - POSTGRES_DB=mattermost
      - POSTGRES_USER=
      - POSTGRES_PASSWORD=
    volumes:
      - pgdata:/var/lib/postgresql/data
volumes:
  pgdata:

Trust and Data Boundaries

The API server trusts only the internal network; user data (messages, posts, channel metadata) lives in PostgreSQL, while binary files are stored in an S3‑compatible bucket. No user data is kept on the Mattermost filesystem beyond temporary caches.

Operational Checks

• Monitor PostgreSQL max_connections and active connections via SELECT count(*) FROM pg_stat_activity;
• Track WebSocket latency: measure round‑trip time from client to /api/v4/websocket endpoint.
• Check object storage health with a simple HEAD request to a test bucket.

Failure Modes

• Database write‑lock during a long migration blocks INSERT into the posts table, causing message delivery to stall while API reads may still succeed.
• Object storage timeout or network partition leaves text chat functional but file uploads return 503 errors.

Conditions that Would Change the Design

1. Horizontal scaling of the Mattermost backend requires sticky sessions at the load balancer to preserve WebSocket affinity.
2. High message volume (>10k msgs/min) demands indexing on posts(create_at, channel_id) and possibly read replicas.
3. Regulatory need for encryption at rest may prompt moving binary storage to a KMS‑managed bucket.