Self-Host Mattermost: Open Source Slack for Teams 2026

TL;DR

Mattermost (MIT, ~30K GitHub stars, Go + React) is a self-hosted team messaging platform that closely mirrors Slack's UX. Channels, threads, mentions, file sharing, slash commands, webhooks, and integrations — all in a self-hosted package. Slack Pro costs $7.25/user/month ($145/month for 20 users). Mattermost Team Edition is free for any team size. The paid Enterprise features (SSO, compliance exports, advanced permissions) are optional.

Key Takeaways

• Mattermost: MIT license, ~30K stars, Go + React — self-hosted, unlimited users free
• Slack UX parity: Channels, DMs, threads, reactions, file sharing, search
• Integrations: Webhooks, slash commands, bots, GitHub/GitLab/Jira integrations
• Mobile apps: iOS and Android apps (free, unofficial builds also available)
• RAM: ~500MB for the app + Postgres
• Enterprise: SSO, compliance export, advanced RBAC available in paid tiers

---

Mattermost vs Matrix vs Slack

Feature	Mattermost CE	Matrix + Synapse	Slack Pro
License	MIT	Apache 2.0	Proprietary
Cost	Free (hosting)	Free (hosting)	$7.25/user/mo
Slack-like UX	Yes (near identical)	Different (Element UI)	Native
Federation	No	Yes (Matrix)	No
E2EE	Beta	Yes	No
Bridging	Limited	30+ bridges	Yes (paid)
LDAP/OIDC	Free (basic)	Yes	Yes
Threads	Yes	Yes	Yes
Calls	Plugin	Element Call	Yes
GitHub Stars	~30K	~12K	—

---

Part 1: Docker Setup

# docker-compose.yml
services:
  postgres:
    image: postgres:16-alpine
    restart: unless-stopped
    volumes:
      - postgres_data:/var/lib/postgresql/data
    environment:
      POSTGRES_DB: mattermost
      POSTGRES_USER: mattermost
      POSTGRES_PASSWORD: "${POSTGRES_PASSWORD}"
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U mattermost"]
      interval: 10s

  mattermost:
    image: mattermost/mattermost-team-edition:latest
    container_name: mattermost
    restart: unless-stopped
    ports:
      - "8065:8065"
    depends_on:
      postgres:
        condition: service_healthy
    volumes:
      - mattermost_config:/mattermost/config
      - mattermost_data:/mattermost/data
      - mattermost_logs:/mattermost/logs
      - mattermost_plugins:/mattermost/plugins
    environment:
      MM_SQLSETTINGS_DRIVERNAME: postgres
      MM_SQLSETTINGS_DATASOURCE: "postgres://mattermost:${POSTGRES_PASSWORD}@postgres:5432/mattermost?sslmode=disable"
      MM_SERVICESETTINGS_SITEURL: "https://chat.yourdomain.com"
      MM_SERVICESETTINGS_LISTENADDRESS: ":8065"

volumes:
  postgres_data:
  mattermost_config:
  mattermost_data:
  mattermost_logs:
  mattermost_plugins:

docker compose up -d

---

Part 2: HTTPS with Caddy

chat.yourdomain.com {
    reverse_proxy localhost:8065
}

Visit https://chat.yourdomain.com → create admin account → create your team.

---

Part 3: Initial Configuration

After first login:

System Console → Site Configuration:

• Site URL: https://chat.yourdomain.com
• Enable invitations: Yes or No
• Allow team creation: Yes (open) or No (admin only)

System Console → Email:

SMTP Server: smtp.yourdomain.com
SMTP Port: 587
SMTP Username: noreply@yourdomain.com
SMTP Password: your-smtp-password

Disable open registration (admin creates accounts or invites): System Console → Authentication → Email → Enable account creation: Off

---

Part 4: Invite and Onboard Team Members

System Console → User Management → Invite People

Or share invite link: https://chat.yourdomain.com/signup_user_complete/?id=TEAM_ID

Bulk import users from CSV:

# Create import file:
cat > users.jsonl << 'EOF'
{"type":"user","user":{"username":"jsmith","email":"jsmith@company.com","first_name":"John","last_name":"Smith"}}
{"type":"user","user":{"username":"alee","email":"alee@company.com","first_name":"Amy","last_name":"Lee"}}
EOF

# Import:
docker exec mattermost ./mattermost import bulk users.jsonl --apply

---

Part 5: Channels and Workspace Setup

Create Channels

In any team:

• + → New Channel → Public or Private
• Suggested channels: #general, #announcements, #engineering, #random, #ops

Channel Types

• Public: Visible and joinable by all team members
• Private: Invite-only, doesn't appear in channel list
• Direct Messages: 1:1 private chat
• Group Messages: Up to 8 people, no channel name

---

Part 6: Webhooks and Integrations

Incoming Webhook (External → Mattermost)

1. Main Menu → Integrations → Incoming Webhooks → Add Incoming Webhook
2. Choose channel
3. Copy webhook URL

# Post to Mattermost from any script:
curl -X POST https://chat.yourdomain.com/hooks/your-webhook-id \
  -H 'Content-Type: application/json' \
  -d '{"text": "Deploy complete for v2.1.0 ✅", "channel": "engineering"}'

Outgoing Webhook (Mattermost → External)

Fire a webhook when a user says a keyword:

1. Integrations → Outgoing Webhooks → Add
2. Trigger word: !deploy
3. Callback URL: your service endpoint
4. When someone types !deploy, Mattermost POSTs to your URL

Slash Commands

Create a custom slash command:

1. Integrations → Slash Commands → Add Slash Command
2. Command: /standup
3. Request URL: https://your-bot.yourdomain.com/standup
4. Usage: Users type /standup → your service gets a request → responds to channel

---

Part 7: GitHub Integration

1. Main Menu → Integrations → GitHub Plugin (or install from marketplace)
2. Set GitHub OAuth App credentials
3. /github connect in any channel to link your GitHub account
4. /github subscribe org/repo — get PR/issue notifications in channel

New PR from jsmith:
Fix login timeout issue (#247)
https://github.com/org/repo/pull/247

---

Part 8: GitLab Notifications

# In GitLab project: Settings → Integrations → Mattermost
# or use generic webhook:

curl https://chat.yourdomain.com/hooks/YOUR_HOOK_ID \
  -d '{"text":"New commit to main by @jsmith: Fix authentication bug"}'

---

Part 9: LDAP / OIDC SSO

Free LDAP (basic): System Console → Authentication → LDAP:

• LDAP Server: ldap.yourdomain.com
• Base DN: dc=yourdomain,dc=com
• Bind Username / Password

OIDC via Authentik (free in Community Edition): System Console → Authentication → OpenID Connect:

• Discovery Endpoint: https://auth.yourdomain.com/application/o/mattermost/.well-known/openid-configuration
• Client ID + Secret from Authentik

---

Part 10: Calls Plugin

Enable voice and screen sharing via the Calls plugin:

1. System Console → Plugin Marketplace → Install Calls
2. Enable the plugin
3. Configure STUN server (uses Google's by default, or self-host coturn)
4. Users can start calls in any channel

---

Maintenance

# Update Mattermost:
docker compose pull
docker compose up -d

# Backup:
docker exec postgres pg_dump -U mattermost mattermost | gzip \
  > mattermost-db-$(date +%Y%m%d).sql.gz

tar -czf mattermost-data-$(date +%Y%m%d).tar.gz \
  $(docker volume inspect mattermost_mattermost_data --format '{{.Mountpoint}}')

# Logs:
docker compose logs -f mattermost

# Admin CLI:
docker exec mattermost ./mattermost user list
docker exec mattermost ./mattermost channel list your-team-name

Why Self-Host Mattermost?

The case for self-hosting Mattermost comes down to three practical factors: data ownership, cost at scale, and operational control.

Data ownership is the fundamental argument. When you use a SaaS version of any tool, your data lives on someone else's infrastructure subject to their terms of service, their security practices, and their business continuity. If the vendor raises prices, gets acquired, changes API limits, or shuts down, you're left scrambling. Self-hosting Mattermost means your data and configuration stay on infrastructure you control — whether that's a VPS, a bare metal server, or a home lab.

Cost at scale matters once you move beyond individual use. Most SaaS equivalents charge per user or per data volume. A self-hosted instance on a $10-20/month VPS typically costs less than per-user SaaS pricing for teams of five or more — and the cost doesn't scale linearly with usage. One well-configured server handles dozens of users for a flat monthly fee.

Operational control is the third factor. The Docker Compose configuration above exposes every setting that commercial equivalents often hide behind enterprise plans: custom networking, environment variables, storage backends, and authentication integrations. You decide when to update, how to configure backups, and what access controls to apply.

The honest tradeoff: you're responsible for updates, backups, and availability. For teams running any production workloads, this is familiar territory. For individuals, the learning curve is real but the tooling (Docker, Caddy, automated backups) is well-documented and widely supported.

Server Requirements and Sizing

Before deploying Mattermost, assess your server capacity against expected workload.

Minimum viable setup: A 1 vCPU, 1GB RAM VPS with 20GB SSD is sufficient for personal use or small teams. Most consumer VPS providers — Hetzner, DigitalOcean, Linode, Vultr — offer machines in this range for $5-10/month. Hetzner offers excellent price-to-performance for European and US regions.

Recommended production setup: 2 vCPUs with 4GB RAM and 40GB SSD handles most medium deployments without resource contention. This gives Mattermost headroom for background tasks, caching, and concurrent users while leaving capacity for other services on the same host.

Storage planning: The Docker volumes in this docker-compose.yml store all persistent Mattermost data. Estimate your storage growth rate early — for data-intensive tools, budget for 3-5x your initial estimate. Hetzner Cloud and Vultr both support online volume resizing without stopping your instance.

Operating system: Any modern 64-bit Linux distribution works. Ubuntu 22.04 LTS and Debian 12 are the most commonly tested configurations. Ensure Docker Engine 24.0+ and Docker Compose v2 are installed — verify with docker --version and docker compose version. Avoid Docker Desktop on production Linux servers; it adds virtualization overhead and behaves differently from Docker Engine in ways that cause subtle networking issues.

Network: Only ports 80 and 443 need to be publicly accessible when running behind a reverse proxy. Internal service ports should be bound to localhost only. A minimal UFW firewall that blocks all inbound traffic except SSH, HTTP, and HTTPS is the single most effective security measure for a self-hosted server.

Backup and Disaster Recovery

Running Mattermost without a tested backup strategy is an unacceptable availability risk. Docker volumes are not automatically backed up — if you delete a volume or the host fails, data is gone with no recovery path.

What to back up: The named Docker volumes containing Mattermost's data (database files, user uploads, application state), your docker-compose.yml and any customized configuration files, and .env files containing secrets.

Backup approach: For simple setups, stop the container, archive the volume contents, then restart. For production environments where stopping causes disruption, use filesystem snapshots or database dump commands (PostgreSQL pg_dump, SQLite .backup, MySQL mysqldump) that produce consistent backups without downtime.

For a complete automated backup workflow that ships snapshots to S3-compatible object storage, see the Restic + Rclone backup guide. Restic handles deduplication and encryption; Rclone handles multi-destination uploads. The same setup works for any Docker volume.

Backup cadence: Daily backups to remote storage are a reasonable baseline for actively used tools. Use a 30-day retention window minimum — long enough to recover from mistakes discovered weeks later. For critical data, extend to 90 days and use a secondary destination.

Restore testing: A backup that has never been restored is a backup you cannot trust. Once a month, restore your Mattermost backup to a separate Docker Compose stack on different ports and verify the data is intact. This catches silent backup failures, script errors, and volume permission issues before they matter in a real recovery.

Security Hardening

Self-hosting means you are responsible for Mattermost's security posture. The Docker Compose setup provides a functional base; production deployments need additional hardening.

Always use a reverse proxy: Never expose Mattermost's internal port directly to the internet. The docker-compose.yml binds to localhost; Caddy or Nginx provides HTTPS termination. Direct HTTP access transmits credentials in plaintext. A reverse proxy also centralizes TLS management, rate limiting, and access logging.

Strong credentials: Change default passwords immediately after first login. For secrets in docker-compose environment variables, generate random values with openssl rand -base64 32 rather than reusing existing passwords.

Firewall configuration:

ufw default deny incoming
ufw allow 22/tcp
ufw allow 80/tcp
ufw allow 443/tcp
ufw enable

Internal service ports (databases, admin panels, internal APIs) should only be reachable from localhost or the Docker network, never directly from the internet.

Network isolation: Docker Compose named networks keep Mattermost's services isolated from other containers on the same host. Database containers should not share networks with containers that don't need direct database access.

VPN access for sensitive services: For internal-only tools, restricting access to a VPN adds a strong second layer. Headscale is an open source Tailscale control server that puts your self-hosted stack behind a WireGuard mesh, eliminating public internet exposure for internal tools.

Update discipline: Subscribe to Mattermost's GitHub releases page to receive security advisory notifications. Schedule a monthly maintenance window to pull updated images. Running outdated container images is the most common cause of self-hosted service compromises.

Troubleshooting Common Issues

Container exits immediately or won't start

Check logs first — they almost always explain the failure:

docker compose logs -f mattermost

Common causes: a missing required environment variable, a port already in use, or a volume permission error. Port conflicts appear as bind: address already in use. Find the conflicting process with ss -tlpn | grep PORT and either stop it or change Mattermost's port mapping in docker-compose.yml.

Cannot reach the web interface

Work through this checklist:

1. Confirm the container is running: docker compose ps
2. Test locally on the server: curl -I http://localhost:PORT
3. If local access works but external doesn't, check your firewall: ufw status
4. If using a reverse proxy, verify it's running and the config is valid: caddy validate --config /etc/caddy/Caddyfile

Permission errors on volume mounts

Some containers run as a non-root user. If the Docker volume is owned by root, the container process cannot write to it. Find the volume's host path with docker volume inspect VOLUME_NAME, check the tool's documentation for its expected UID, and apply correct ownership:

chown -R 1000:1000 /var/lib/docker/volumes/your_volume/_data

High resource usage over time

Memory or CPU growing continuously usually indicates unconfigured log rotation, an unbound cache, or accumulated data needing pruning. Check current usage with docker stats mattermost. Add resource limits in docker-compose.yml to prevent one container from starving others. For ongoing visibility into resource trends, deploy Prometheus + Grafana or Netdata.

Data disappears after container restart

Data stored in the container's writable layer — rather than a named volume — is lost when the container is removed or recreated. This happens when the volume mount path in docker-compose.yml doesn't match where the application writes data. Verify mount paths against the tool's documentation and correct the mapping. Named volumes persist across container removal; only docker compose down -v deletes them.

Keeping Mattermost Updated

Mattermost follows a regular release cadence. Staying current matters for security patches and compatibility. The update process with Docker Compose is straightforward:

docker compose pull          # Download updated images
docker compose up -d         # Restart with new images
docker image prune -f        # Remove old image layers (optional)

Read the changelog before major version updates. Some releases include database migrations or breaking configuration changes. For major version bumps, test in a staging environment first — run a copy of the service on different ports with the same volume data to validate the migration before touching production.

Version pinning: For stability, pin to a specific image tag in docker-compose.yml instead of latest. Update deliberately after reviewing the changelog. This trades automatic patch delivery for predictable behavior — the right call for business-critical services.

Post-update verification: After updating, confirm Mattermost is functioning correctly. Most services expose a /health endpoint that returns HTTP 200 — curl it from the server or monitor it with your uptime tool.

---

See all open source team communication tools at OSSAlt.com/alternatives/slack.

See open source alternatives to Mattermost on OSSAlt.