Lagoon – Simple Linux package repository mirror

A lagoon is a shallow stretch of water separated from the sea by a reef or sandbank. Lagoon can be used to mirror package repositories or parts of these repositories from the internet hence the name Lagoon.

When running Linux servers in an enterprise environment it is useful to have all servers running the same versions of software. In order to accomplish this, package repositories must be frozen at a certain point in time because normal (public) repositories are constantly updated and ‘on the move’.

Lagoon can be used to set up a local mirror for upstream OS package repositories and makes it possible to capture certain points in time or so called snapshots. It also provides the latest snapshot or version of the upstream repository. Lagoon is only capable of providing very basic functionality and is not a replacement for Red Hat’s Satellite, Foreman’s Katello or Pulp.

Lagoon synchronizes with the remote repository and stores the files in the upstream folder. When synchronization is complete a point in time snapshot is made in the staging folder according to the following pattern 20060102 (therefore the snapshot resolution cannot be smaller than a day). After the point in time snapshot is created, it is published in the public folder using the same pattern. The last snapshot is also published as latest.

Running Lagoon

Lagoon can be run as a standalone golang binary or from a Docker container. A Docker Compose file is included for reference.

Run Lagoon from a Docker container:

docker run --name lagoon -v $PWD/lagoon.yml:/etc/lagoon/lagoon.yml lagoon:latest


The following dependencies are needed for running Lagoon:

  • rsync
  • yum-utils
  • createrepo

Supported synchronisation methods

Sync method Supported Status
Rsync yes
RPM reposync beta Basic sync. TODO: implement errata support

File storage

The treeview below shows how snapshots are stored, for example repo1 consists of daily snapshots and repo2 consists of weekly snapshots. Each folder contains the files which were downloaded from the upstream repository at that certain moment in time. Hardlinks are being used for efficient storage and to make sure files do not disappear from a staging snapshot when they are deleted from the upstream content. Staging snapshots are published with symlinks, the latest snapshot always points to the last staging snapshot.

|-- public
|   |-- repo1
|   |   |-- 20220126 -> /var/lib/lagoon/staging/repo1/20220126
|   |   |-- 20220127 -> /var/lib/lagoon/staging/repo1/20220127
|   |   |-- 20220128 -> /var/lib/lagoon/staging/repo1/20220128
|   |   |-- 20220129 -> /var/lib/lagoon/staging/repo1/20220129
|   |   |-- 20220130 -> /var/lib/lagoon/staging/repo1/20220130
|   |   `-- latest -> /var/lib/lagoon/staging/repo1/20220130
|   `-- repo2
|       |-- 20220115 -> /var/lib/lagoon/staging/repo2/20220115
|       |-- 20220122 -> /var/lib/lagoon/staging/repo2/20220122
|       |-- 20220129 -> /var/lib/lagoon/staging/repo2/20220129
|       `-- latest -> /var/lib/lagoon/staging/repo2/20220129
|-- staging
|   |-- repo1
|   |   |-- 20220126
|   |   |-- 20220127
|   |   |-- 20220128
|   |   |-- 20220129
|   |   `-- 20220130
|   `-- repo2
|       |-- 20220115
|       |-- 20220122
|       `-- 20220129
`-- upstream
    |-- repo1
    |   |-- file_1
    |   `-- file_n
    `-- repo2
        |-- file_1
        `-- file_n

Lagoon can also take care of automatically freeing up diskspace by removing snapshots which aren’t used anymore. This can be configured by telling Lagoon how much snapshots it has to keep for a certain repository.


See lagoon.example.yml for example configuration.

  - id: docker-ce_centos-7 # Unique id
    # Name of the repo
    name: Docker CE CentOS 7 x86_64
    # Type of remote repository (rsync or reposync)
    type: reposync
    # Upstream rsync url or reposync multiline string with yum repo config
    src: |
      baseurl =
      enabled = 1
      gpgcheck = 1
      gpgkey =
      name = Docker CE Stable - x86_64
    # Destination the repo (absolute path)
    dest: /var/lib/lagoon
    # Cron sync expression see:
    cron: "*/10 * * * * *"
    # Number of snapshots to keep
    snapshots: 52
    # List of directories to exclude from rsync
    #exclude: []

Logging and monitoring

By default Lagoon logs to stdout using JSON format. In order to enable debug logging start Lagoon with -d parameter. For human readable logging start Lagoon with -h parameter. Each separate sync job can be identified by the repository name and a unique ID.

Lagoon can be monitored with Prometheus and exposes its metrics on port 9000 at /metrics. In addition to the standard golang metrics the following Lagoon specific metrics are exposed:

Metric Description
lagoon_sync_total The total number of repo syncs
lagoon_sync_duration_seconds The sync duration

Building Lagoon

We will use Docker as a build environment so local installation of build tools is not required. Execute the commands from the root of the project.

Building a Docker image:

docker build -f build/Dockerfile -t lagoon .

You can either run a Docker container from the image or use the following command to extract the lagoon binary to run it separately:

docker run --rm -v $PWD:/build lagoon cp /etc/lagoon/lagoon /build

Developing Lagoon

The preferred method for developing Lagoon is using VSCode with the ‘Remote – Containers’ extension ms-vscode-remote.remote-containers. A .devcontainer context is included with the project in order to open it in a remote container and get your development environment up-and-running quickly.


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