Kopia with Docker Compose

What Kopia needs

Only figures Kopia's own documentation publishes, each linked to the page it is on. Where the project gives no number, this page does not invent one.

On top of this, Caddy (the reverse proxy in the file) is a single small container.

Which hardware Kopia has images for

Read from each image's manifest list in its registry (anonymous, read-only) when this page was built. An app counts for a CPU only if every one of its images lists it.

• x86-64 PC or NAS (linux/amd64): every image has a build.
• Raspberry Pi 4/5, 64-bit OS (linux/arm64): every image has a build.
• Raspberry Pi 3 or Zero 2 W, 32-bit OS (linux/arm/v7): every image has a build.

A manifest says an image exists for a CPU, not how well Kopia runs on it: a build for arm64 or arm/v7 can still be too slow or need more memory than the board has. The RAM and disk Kopia publishes are in the table above and, for a whole set of apps against a Raspberry Pi, on Will it run on my machine?. A tag like latest can move to a new digest after the date checked.

docker-compose.yml

This is exactly what the builder writes for Kopia alone on example.org: the official definition with its published ports removed and Caddy added in front. Every ${VARIABLE} is defined in the .env below.

# docker-compose.yml built at dankhost.com for: Kopia
# Each app block is its official compose definition. Only the names were prefixed with
# the app slug (services, containers, volumes, bind folders, .env variables) so any set of
# apps can share one file; other differences are listed under "Changed:" in each block.
# Only Caddy publishes ports. Secrets live in .env next to this file.

services:
  # ---- Caddy: the one reverse proxy, HTTPS certificates from Let's Encrypt ----
  # Source: https://caddyserver.com/docs/running (checked 2026-09-23)
  # Source: https://github.com/dani-garcia/vaultwarden/wiki/Using-Docker-Compose (checked 2026-09-23)
  # Caddyfile goes in ./caddy/Caddyfile. Fixed address 172.30.0.2 so apps can trust it exactly.
  caddy:
    image: "caddy:2"
    container_name: "caddy"
    restart: "unless-stopped"
    ports:
      - "80:80"
      - "443:443"
      - "443:443/udp"
    volumes:
      - "./caddy:/etc/caddy"
      - "caddy-data:/data"
      - "caddy-config:/config"
    networks:
      proxy:
        ipv4_address: "172.30.0.2"

  # ---- Kopia (backup.example.org) ----
  # Source: https://kopia.io/docs/installation/ (checked 2026-09-26)
  # Source: https://github.com/kopia/kopia/blob/master/cli/command_server_start.go (checked 2026-09-26)
  # Changed: Removed the '51515:51515' port; Caddy reaches kopia:51515 on the proxy network. The obsolete version: '3.7' line and container_name Kopia are left out.
  #          The /path/to/... folders are ./config, ./cache, ./logs, ./data (read-only: what Kopia may back up), ./repository and ./tmp. hostname and USER, which Kopia records with every snapshot, are kopia instead of the placeholders Hostname and User.
  #          The web UI user is kopia and its password (--server-password) and the repository password (KOPIA_PASSWORD) are generated instead of USERNAME, SECRET_PASSWORD and SECRET.
  kopia:
    image: "kopia/kopia:latest"
    container_name: "kopia"
    hostname: "kopia"
    restart: "unless-stopped"
    command:
      - "server"
      - "start"
      - "--disable-csrf-token-checks"
      - "--insecure"
      - "--address=0.0.0.0:51515"
      - "--server-username=kopia"
      - "--server-password=${KOPIA_SERVER_PASSWORD}"
    environment:
      KOPIA_PASSWORD: "${KOPIA_REPOSITORY_PASSWORD}"
      USER: "kopia"
    volumes:
      - "./kopia/config:/app/config"
      - "./kopia/cache:/app/cache"
      - "./kopia/logs:/app/logs"
      - "./kopia/data:/data:ro"
      - "./kopia/repository:/repository"
      - "./kopia/tmp:/tmp:shared"
    networks:
      proxy: {}

networks:
  # Pinned so the trusted-proxy address given to each app (172.30.0.2) is exact.
  # If "docker compose up" reports "Pool overlaps", change 172.30.0 here, in Caddy's
  # ipv4_address and in every trusted-proxy value to a free 172.x.0 range.
  proxy:
    ipam:
      config:
        - subnet: "172.30.0.0/24"
          ip_range: "172.30.0.128/25"
          gateway: "172.30.0.1"

volumes:
  caddy-data:
  caddy-config:

Caddyfile save as caddy/Caddyfile

Caddy gets and renews the HTTPS certificate for backup.example.org by itself once the DNS record points at your server and ports 80 and 443 reach it.

# Caddyfile built at dankhost.com. Save it as ./caddy/Caddyfile next to docker-compose.yml.
# Caddy gets and renews a Let's Encrypt certificate for each name below by itself,
# once the DNS records point at this server and ports 80 and 443 reach it.

# Kopia
backup.example.org {
	reverse_proxy kopia:51515
}

.env

The secrets are left blank here on purpose: a password printed on a public page is the same for everyone who copies it. The builder fills them with random letters and digits made in your browser.

# .env for Kopia, from dankhost.com/app/kopia/. Fill the blank secrets before starting.
# Keep this file private (chmod 600).

# Kopia
# 24 random letters and digits: the builder fills this in your browser
KOPIA_SERVER_PASSWORD=
# 32 random letters and digits: the builder fills this in your browser
KOPIA_REPOSITORY_PASSWORD=

Changes from the official file

Besides prefixing every service, container, volume, folder and variable with kopia (so any set of apps can share one file), these are all the differences from what the project documents:

• Removed the '51515:51515' port; Caddy reaches kopia:51515 on the proxy network. The obsolete version: '3.7' line and container_name Kopia are left out.
• The /path/to/... folders are ./config, ./cache, ./logs, ./data (read-only: what Kopia may back up), ./repository and ./tmp. hostname and USER, which Kopia records with every snapshot, are kopia instead of the placeholders Hostname and User.
• The web UI user is kopia and its password (--server-password) and the repository password (KOPIA_PASSWORD) are generated instead of USERNAME, SECRET_PASSWORD and SECRET.

Notes for Kopia behind the proxy

• Log in at https://backup.example.org as kopia with KOPIA_SERVER_PASSWORD from .env.
• In the web UI, create a repository. For a Local Directory repository give the path /repository (./kopia/repository on the server). When it asks for the repository password, use KOPIA_REPOSITORY_PASSWORD from .env, which the container also reads as KOPIA_PASSWORD. Without that password no snapshot can be read.
• Put what you want backed up under ./kopia/data, or change that mount to the folder you want to protect (keep :ro), then add /data as a snapshot source.
• A repository in ./kopia/repository is on the same disk as your data: it protects against deleted or damaged files, not against a failed disk. The README lists S3-compatible storage, Backblaze B2, SFTP, WebDAV and more as repository locations.
• --insecure and --disable-csrf-token-checks come from the documented compose file; Kopia's source describes --insecure as "Allow insecure configurations (do not use in production)" and the CSRF switch as for development/debugging. Here --insecure means Kopia itself speaks plain HTTP inside the Docker network, and Caddy adds HTTPS. Kopia still asks for the web UI password.
• Only the web UI goes through the proxy. Kopia clients on other machines that would use this server as a repository server speak gRPC; the installation page gives an nginx grpc_pass example, and this file does not set that up.
• ./kopia/tmp is mounted with :shared, as the page asks, so snapshots you mount in the UI are visible on the host. Docker refuses :shared on a folder whose mount is not shared; if "docker compose up" says so, remove that mount and you lose only browsing mounted snapshots.

Back it up

Kopia is itself the backup tool. What to keep of it: /app/config with repository.config (how to reach the repository), the repository folder when it is local, and the repository password, which is in .env and without which no snapshot can be read.

Below is the BACKUP.md the builder writes next to the compose file above: which of its folders and volumes hold data, what to copy with which container stopped, and a restore check. Pick more apps in the builder and it covers them all in one file.

# BACKUP.md built at dankhost.com for: Kopia

What to copy from the docker-compose.yml built with this file, the database dump each project documents (rewritten for the service names in that file), what to copy with which container stopped, and how to check the result. Run every command in the folder that holds docker-compose.yml.

The folders are owned by the containers' users: put sudo in front of tar if it says "Permission denied". Named volumes live under /var/lib/docker/volumes, not next to the compose file, so they are copied through a throwaway ubuntu container (Docker's documented --volumes-from method). tar makes a full copy each run; for large folders an incremental tool (restic, borg, rsync) saves time and space.

Never run "docker compose down -v" on this file: it deletes the named volumes of every app in it.

## Before you start

    BACKUP=/mnt/backup/selfhost   # change this: a disk or machine other than this server's system disk
    mkdir -p "$BACKUP"

## Every time: the three stack files

    tar czf "$BACKUP/stack-files.tar.gz" docker-compose.yml .env caddy

.env holds the database passwords and secret keys the apps were set up with; keep this archive as private as the data.

## Caddy (the reverse proxy)

Caddy's docs: 'The data directory must not be treated as a cache.' It holds the TLS certificates and their private keys; without it Caddy has to ask Let's Encrypt for every certificate again.

- caddy-data (named volume, /data in caddy)
  BACK UP: TLS certificates, private keys, OCSP staples.
- caddy-config (named volume, /config in caddy)
  SKIP: the last active configuration, kept for 'caddy run --resume', which this setup does not use: it starts from the Caddyfile.
- ./caddy (/etc/caddy in caddy)
  IN stack-files.tar.gz: the Caddyfile, copied with the stack files above.

Copy (Caddy keeps serving while you copy):

    docker run --rm --volumes-from caddy -v "$BACKUP":/backup ubuntu tar cvf /backup/caddy-data.tar /data

Restore check:

    tar tf "$BACKUP/caddy-data.tar" > /dev/null && echo OK
    docker run --rm --volumes-from caddy -v "$BACKUP":/backup ubuntu bash -c "cd /data && tar xvf /backup/caddy-data.tar --strip 1"

Sources:
- Caddy docs: Conventions, Data directory: https://caddyserver.com/docs/conventions#data-directory (checked 2026-09-24)
- Docker docs: Volumes, Back up, restore, or migrate data volumes: https://docs.docker.com/engine/storage/volumes/#back-up-restore-or-migrate-data-volumes (checked 2026-09-24)

## Kopia

Kopia is itself the backup tool. What to keep of it: /app/config with repository.config (how to reach the repository), the repository folder when it is local, and the repository password, which is in .env and without which no snapshot can be read.

What this compose mounts:
- ./kopia/config (/app/config in kopia)
  BACK UP: repository.config and the server's settings.
- ./kopia/cache (/app/cache in kopia)
  SKIP: a cache of downloaded repository data; Kopia fills it again.
- ./kopia/logs (/app/logs in kopia)
  SKIP: log files.
- ./kopia/data (/data in kopia)
  YOUR FILES: the folders Kopia backs up (read-only).
- ./kopia/repository (/repository in kopia)
  OPTIONAL: the snapshots themselves, for a Local Directory repository. A copy on another disk or machine is what protects them from this disk failing.
- ./kopia/tmp (/tmp in kopia)
  SKIP: where mounted snapshots appear while you browse them.

YOUR FILES folders hold your own media, not Kopia data. If this server has the only copy, back them up like any other files; the steps below leave them out.

1. Stop kopia. Stopping it keeps a running snapshot from writing to the repository mid-copy.

    docker compose stop kopia

2. Copy while kopia is stopped:

    tar czf "$BACKUP/kopia-config.tar.gz" ./kopia/config

3. Start it again:

    docker compose start kopia

Restore check:

    tar tzf "$BACKUP/kopia-config.tar.gz" > /dev/null && echo OK

Put a copy back (with kopia stopped):

    tar xzf "$BACKUP/kopia-config.tar.gz"   # recreates ./kopia/config; move the old folder aside first

Stop it, put ./kopia/config (and ./kopia/repository if you copied it) back, start it. The repository opens only with the same KOPIA_REPOSITORY_PASSWORD from .env.

Sources:
- Kopia docs: Installation, Docker Images (server-mode docker-compose, mounts, KOPIA_PASSWORD): https://kopia.io/docs/installation/ (checked 2026-09-26)
- Docker docs: Volumes, Back up, restore, or migrate data volumes: https://docs.docker.com/engine/storage/volumes/#back-up-restore-or-migrate-data-volumes (checked 2026-09-26)

Sources

Every page below was fetched on the date shown.

• Kopia README on GitHub checked 2026-09-26 (what it does)
• Kopia docs: Installation, Docker Images (server-mode docker-compose, mounts, KOPIA_PASSWORD) checked 2026-09-26 (compose definition and proxy settings, backup plan)
• Kopia source: server start flags (--insecure, --disable-csrf-token-checks) checked 2026-09-26 (compose definition and proxy settings)
• Caddy docs: Keep Caddy running (Docker Compose section) checked 2026-09-23 (Caddy)
• Vaultwarden wiki: Caddy with HTTP challenge (uses the caddy:2 image) checked 2026-09-23 (Caddy)
• Docker docs: Volumes, Back up, restore, or migrate data volumes checked 2026-09-26 (backup plan)
• Caddy docs: Conventions, Data directory checked 2026-09-24 (backup plan)

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