The CernVM-FS Repository Gateway and Publishers

This page describes the distributed CernVM-FS publication architecture, composed of a repository gateway machine and separate publisher machines.

Glossary

Publisher

A machine running the CernVM-FS server tools which can publish to a number of repositories, using a repository gateway as mediator.

The resource-intensive parts of the publication operation take place here: compressing and hashing the files which are to be added or modified. The processed files are then packed together and sent to the gateway to be inserted into the repository and made available to clients.

Repository gateway

This machine runs the cvmfs-gateway application. It is the sole entity able to write to the authoritative storage of the managed repositories, either by mounting the storage volume or through an S3 API.

The role of the gateway is to mediate access to a set of repositories by assigning exclusive leases for specific repository sub-paths to different publisher machines. The gateway receives payloads from publishers, in the form of object packs, which it processes and writes to the repository storage. Its final task is to rebuild the catalogs and repository manifest of the modified repositories at the end of a successful publication transaction.

Repository gateway configuration

The cvmfs-gateway application needs to run on the gateway machine. The application is currently packaged for CentOS 7, SLC 6, and Ubuntu 16.04 and 18.04.

When the CernVM-FS client and server packages are also installed, it’s possible to use the gateway machine as a “master” publisher, reserved for performing some initial repository transformations, before a separate publisher machine is set up. To avoid any possible repository corruption, the gateway application should always be stopped before opening a repository transaction on the gateway machine.

With the gateway application installed, create the repository which will be used for the rest of this guide:

# cvmfs_server mkfs -o root test.cern.ch

Create an API key file for the new repo (replace <KEY_ID> and <SECRET> with actual values):

# cat <<EOF > /etc/cvmfs/keys/test.cern.ch.gw
plain_text <KEY_ID> <SECRET>
EOF
# chmod 600 /etc/cvmfs/keys/test.cern.ch.gw

Since version 1.0 of cvmfs-gateway, the repository and key configuration have been greatly simplified. If an API key file is present at the conventional location (/etc/cvmfs/keys/<REPOSITORY_NAME>.gw), it will be used by default as the key for that repository. The repository configuration file only needs to specify which repositories are to be handled by the application:

# cat <<EOF > /etc/cvmfs/gateway/repo.json
{
  "version": 2,

  "repos": [
    "test.cern.ch"
  ]
}
EOF

The "version": 2 property enables the use of the improved configuration syntax. If this property is omitted, the parser will interpret the file using the legacy configuration syntax, maintaining compatibility with existing configuration files (see Legacy repository configuration syntax). The Advanced repository configuration section shows how to implement more complex key setups.

In addition to repo.json, the user.json configuration file contains runtime parameters for the gateway application. The most important are:

  • max_lease_time - the maximum duration, in seconds, of an acquired lease
  • port - the TCP port on which the gateway application listens, 4929 by default (the legacy name for this option is “fe_tcp_port”)
  • num_receivers - the number of parallel cvmfs_receiver worker

processes to be spawned. Default value is 1, and it should not be increased beyond the number of available CPU cores (the legacy name of this option is the size entry in the receiver_config map).

To access the gateway service API, the specified port needs to be open in the firewall. If the gateway machine also serves as a repository stratum 0 (i.e. the repository is created with “local” upstream), then port 80/TCP also needs to be open.

Finally, to start the gateway application, use systemctl if systemd is available:

# systemctl start cvmfs-gateway.service

otherwise use the service command:

# service cvmfs-gateway start

Note that in order to apply any gateway configuration changes, including changes to the API keys, the gateway service must be restarted.

If systemd is available, the application logs can be consulted with:

# journalctl -u cvmfs-gateway

On CentOS 6, where systemd is not available, the log file can be accessed directly at /var/log/cvmfs-gateway.log.

Running under a different user

By default, the cvmfs-gateway application is run as root. An included systemd service template file allows running it as an arbitrary user:

# systemctl start cvmfs-gateway@<USER>

To consult the logs of the application instance running as <USER>, run:

# journalctl -u cvmfs-gateway@<USER>

Publisher configuration

This section describes how to set up a publisher for a specific CVMFS repository. The precondition is a working gateway machine where the repository has been created as a Stratum 0.

  • The gateway machine is gateway.cern.ch.
  • The publisher is publisher.cern.ch.
  • The new repository’s fully qualified name is test.cern.ch.
  • The repository’s public key (RSA) is test.cern.ch.pub.
  • The repository’s public key (encoded as a X.509 certificate) is test.cern.ch.crt.
  • The gateway API key is test.cern.ch.gw.
  • The gateway application is running on port 4929 at the URL http://gateway.cern.ch:4929/api/v1.
  • The three keys for the repository (.pub, .crt, and .gw) have been copied from the gateway machine onto the publisher machine, in the directory /tmp/test.cern.ch_keys/.

To make the repository available for writing on publisher.cern.ch, run the following command on that machine as an unprivileged user with sudo access:

$ sudo cvmfs_server mkfs -w http://gateway.cern.ch/cvmfs/test.cern.ch \
                         -u gw,/srv/cvmfs/test.cern.ch/data/txn,http://gateway.cern.ch:4929/api/v1 \
                         -k /tmp/test.cern.ch_keys -o `whoami` test.cern.ch

At this point, it’s possible to start writing into the repository from the publisher machine:

$ cvmfs_server transaction test.cern.ch

Alternatively, to take advantage of the gateway functionality which allows concurrent transactions on different paths of a repository, or fine-grained permission to only publish changes in certain paths, you can request a publishing lease that is scoped to a subdirectory of the repository by starting a transaction like this:

$ cvmfs_server transaction test.cern.ch/example/path

Then to commit the changes to the repository and publish:

$ cvmfs_server publish

Querying the gateway machine

The configuration and current state of the gateway application can be queried using standard HTTP requests. A “GET” request to the “repos” endpoint returns the key configuration for all the repositories:

$ curl http://example.gateway.org:4929/api/v1/repos | jq

{
  "data": {
    "example.repo.org": {
      "key1": "/"
    }
  },
  "status": "ok"
}

The configuration of a single repository can also be obtained:

$ curl http://example.gateway.org:4929/api/v1/repos/example.repo.org | jq

{
  "data": {
    "key1": "/"
  },
  "status": "ok"
}

The list of current active leases can be obtained as follows:

$ curl http://example.gateway.org:4929/api/v1/leases | jq

{
  "data": {
    "example.repo.org/sub/dir/1": {
      "key_id": "key1",
      "expires": "2019-05-09 23:10:31.730136676 +0200 CEST"
    },
    "example.repo.org/sub/dir/2": {
      "key_id": "key1",
      "expires": "2019-05-09 23:10:32.497061458 +0200 CEST"
    },
    "example.repo.org/sub/dir/3": {
      "key_id": "key1",
      "expires": "2019-05-09 23:10:31.935336579 +0200 CEST"
    }
  },
  "status": "ok"
}

Advanced repository configuration

It’s possible to register multiple API keys with each repository, and each key can be restricted to a specific subpath of the repository:

{
  "version": 2,
  "repos" : [
    {
      "domain": "test.cern.ch",
      "keys": [
        {
          "id": "keyid1",
          "path": "/"
        },
        {
          "id": "keyid2",
          "path": "/restricted/to/subdir"
        }
      ]
    }
  ]
}

Keys can be either be loaded from a file, or declared inline:

{
  "version": 2,
  "keys": [
    {
      "type": "file",
      "file_name": "/etc/cvmfs/keys/test.cern.ch.gw"
    },
    {
      "type": "plain_text",
      "id": "keyid2",
      "secret": "<SECRET>"
    }
  ]
}

The "version": 2 property needs to be specified for this configuration format to be accepted.

It should be noted that when keys are loaded from a file, an id field needs not be specified in the configuration file. The public id of the loaded key is the one specified in the key file itself.

Legacy repository configuration syntax

In the legacy repository configuration format, subpath restrictions are given with the key declaration, not when associating the keys with the repository:

{
  "repos": [
    {
      "domain": "test.cern.ch",
      "keys": ["<KEY_ID>"]
    }
  ],
  "keys": [
    {
      "type": "file",
      "file_name": "/etc/cvmfs/keys/test.cern.ch.gw",
      "repo_subpath": "/"
    }
  ]
}

Updating from cvmfs-gateway-0.2.5

In the first published version, cvmfs-gateway-0.2.5, the application files were installed under /opt/cvmfs-gateway and the database files under /opt/cvmfs-mnesia. Starting with version 0.2.6, the application is installed under /usr/libexec/cvmfs-gateway, while the database files are under /var/lib/cvmfs-gateway.

When updating from 0.2.5, please make sure that the application is stopped:

# systemctl stop cvmfs-gateway

and rerun the setup script:

# /usr/libexec/cvmfs-gateway/scripts/setup.sh

At this point, the new version of the application can be started. If the old directories are still present, they can be deleted:

# rm -r /opt/cvmfs-{gateway,mnesia}