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

Install the cvmfs-gateway package on the gateway machine. Packages for various platforms are available for download here.

When the CernVM-FS client and server packages are also installed and set up as a stratum 0, it’s possible to use the gateway machine as a master publisher (for example to perform some initialization operations on a repository, before a separate publisher machine is set up). To avoid any possible repository corruption, the gateway application should always be stopped before starting a local 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 the port on which httpd listens (80 by default) also needs to be open for TCP.

Note

The gateway service receives data from publishers via HTTP transport. However, since the gateway and publisher have a shared secret (the API key), it is not strictly necessary to use TLS certificates and HTTPS to secure the connection to the gateway. Instead, to ensure the integrity and authenticity of content during the publishing process, a hash-based message authentication code (HMAC) is produced by a publisher, and verified by the gateway.

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

Additional log files may also be found in /var/log/cvmfs-gateway and /var/log/cvmfs-gateway-runner.

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.

Example procedure

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 an 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 key files 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 a non-root 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. When there are multiple keys for the same repository, and they are defined as files, naturally they can not all have the same filename, so at least some of them will be in a location not automatically imported by the gateway. For this reason, all the key file names need to be explicitly enumerated. Keys can also be declared inline. The "version": 2 property needs to be specified for this configuration format to be accepted:

{
  "version": 2,
  "repos": [
    {
      "domain": "test.cern.ch",
      "keys": [
        {
          "id": "keyid1",
          "path": "/"
        },
        {
          "id": "keyid2",
          "path": "/restricted/to/subdir"
        }
      ]
    }
  ],
  "keys": [
    {
      "type": "file",
      "file_name": "/etc/cvmfs/keys/test.cern.ch.gw"
    },
    {
      "type": "plain_text",
      "id": "keyid2",
      "secret": "<SECRET>"
    }
  ]
}

It should be noted that when keys are loaded from a file, an id field does not need to 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}

API reference

This section describes the HTTP API exposed by the gateway application.

Repositories

GET /repos

Retrieve the list of all configured repositories

Response

{
  "data": {
    "test1.cern.ch": {
      "keys": {
        "k1": "/"
      },
      "enabled": true
    }
  },
  "status": "ok"
}

GET /repos/<REPO_NAME>

Retrieve the configuration for a repository

Response

{
  "data": {
    "keys": {
      "k1": "/"
    },
    "enabled": true
  },
  "status": "ok"
}

Leases

GET /leases

Retrieve the current list of leases

Response

{
  "data": {
    "test1.cern.ch/": {
      "key_id": "k1",
      "expires": "2021-10-25 22:02:12.688703553 +0000 UTC"
    }
  },
  "status": "ok"
}

GET /leases/<TOKEN>

Retrieve information about the lease identified by the given token

Response

{
  "data": {
    "key_id": "k1",
    "path": "test1.cern.ch/",
    "expires": "2021-10-25 22:14:12.695939889 +0000 UTC"
  }
}

POST /leases

Request a new lease

Headers

Header	Value	Description
`Authorization`	“<KEY_ID> <HMAC>”	“<KEY_ID>” identifies a gateway key used to sign the message and “<HMAC>” is the keyed-hash message authentication code (HMAC) of the request body.

Request parameters

Parameter	Example value	Description
`api_version`	“3”	API version requested by the client (passed as a string)
`path`	“test1.cern.ch/path/to/lease”	Repository subpath on which a lease is requested

Response

Outcome	Field	Value	Description
Success	`status`	“ok”	Response status
	`session_token`	“<TOKEN>”	String containing the session token associated with the new lease
	`max_api_version`	3	Max API version usable for the remainder of the session
Path busy	`status`	“path_busy”	There is a conflicting lease for the requested path
	“time_remaining”	1234	Remaining lease time in seconds
Error	`status`	“error”	An error occurred
	`reason`	“Something went wrong”	Description text of the error

POST /leases/<TOKEN>

Commit all changes associated with a lease

Headers

Header	Value	Description
`Authorization`	“<KEY_ID> <HMAC>”	“<KEY_ID>” identifies a gateway key used to sign the message and “<HMAC>” is the keyed-hash message authentication code (HMAC) of the request’s path component (`/lease/<TOKEN>`).

Request parameters

Parameter	Example value	Description
`old_root_hash`	“abcd3f”	Initial root hash of the repository
`new_root_hash`	“bfa42b”	New root hash of the repository
`tag name`	“Monday”	Tag associated with the publication
`tag_channel`	“Nightlies”	Name of the publication channel
`tag_description`	“Nightly builds, Monday’s batch”	Description of the tag

Response

Outcome	Field	Value	Description
Success	`status`	“ok”	Response status
	`final_revision`	1234	New revision of the repository after committing the changes associated with a lease
Error	`status`	“error”	An error occurred
	`reason`	“Something went wrong”	Description text of the error

DELETE /leases/<TOKEN>

Cancel a lease

Headers

Header	Value	Description
`Authorization`	“<KEY_ID> <HMAC>”	“<KEY_ID>” identifies a gateway key used to sign the message and “<HMAC>” is the keyed-hash message authentication code (HMAC) of the request’s path component (`/lease/<TOKEN>`).

Response

Outcome	Field	Value	Description
Success	`status`	“ok”	Response status
Error	`status`	“error”	An error occurred
	`reason`	“Something went wrong”	Description text of the error

Payload submission

POST /payloads (deprecated)

Upload an object pack payload

Headers

Header	Value	Description
`Authorization`	“<KEY_ID> <HMAC>”	“<KEY_ID>” identifies a gateway key used to sign the message and “<HMAC>” is the keyed-hash message authentication code (HMAC) of the JSON message at the start of the request body.
`message-size`	1234	Total length of the JSON message at the start of the request body

Request parameters

Parameter	Example value	Description
`session_token`	“<SESSION_TOKEN>”	Session token associated with the lease
`payload_digest`	“bfa42b”	Digest of the payload part (serialized object pack) of the request
`header_size`	1234	Size of the payload header (the header of the serialized object pack)
`api_version`	“3”	API version tag (unused)

The upload payload (the serialized object pack) comes after the JSON part of the message.

Response

Outcome	Field	Value	Description
Success	`status`	“ok”	Response status
Error	`status`	“error”	An error occurred
	`reason`	“Something went wrong”	Description text of the error

POST /payloads/<TOKEN>

Upload an object pack payload

Headers

Header	Value	Description
`Authorization`	“<KEY_ID> <HMAC>”	“<KEY_ID>” identifies a gateway key used to sign the message and “<HMAC>” is the keyed-hash message authentication code (HMAC) of the session token.
`message-size`	1234	Total length of the JSON message at the start of the request body

Request parameters

Parameter	Example value	Description
`payload_digest`	“bfa42b”	Digest of the payload part (serialized object pack) of the request
`header_size`	1234	Size of the payload header (the header of the serialized object pack)
`api_version`	“3”	API version tag (unused)

The upload payload (the serialized object pack) comes after the JSON part of the message.

Response

Outcome	Field	Value	Description
Success	`status`	“ok”	Response status
Error	`status`	“error”	An error occurred
	`reason`	“Something went wrong”	Description text of the error

Notifications

POST /notifications/publish

Publish a notification

Request parameters

Parameter	Example value	Description
`version`	1	API version tag (unused)
`timestamp`	“26 Oct 2021 15:00:00”	Timestamp
`type`	“activity”	Message type (no other values are currently used)
`repository`	“test.cern.ch”	Repository name
`manifest`	“<MANIFEST STRING>”	The serialized signed repository manifest

Response

Outcome	Field	Value	Description
Success	`status`	“ok”	Response status
Error	`status`	“error”	An error occurred
	`reason`	“Something went wrong”	Description text of the error

GET /notifications/subscribe

Subscribe to notifications

Request parameters

Parameter	Example value	Description
`version`	1	API version tag (unused)
`repository`	“test.cern.ch”	Target repository name

This request opens a long-running connection to the notification server. Messages are delivered as server-sent events (SSE), one per line:

data: <JSON MESSAGE>

Messages

Parameter	Example value	Description
`version`	1	API version tag (unused)
`timestamp`	“26 Oct 2021 15:00:00”	Timestamp
`type`	“activity”	Message type (no other values are currently used)
`repository`	“test.cern.ch”	Repository name
`manifest`	“<MANIFEST STRING>”	The serialized signed repository manifest

Publication workflow

sequenceDiagram participant Pub as Publisher participant GW as Gateway Services participant Receiver as Receiver process participant S0 as Stratum 0 Note right of Pub: Request lease for a path in the repository Note right of Pub: $ cvmfs_server transaction test.cern.ch/some/path Pub ->> GW: POST /api/v1/leases GW ->> Pub: <TOKEN> (Session token for lease) Note right of Pub: Make changes on the publisher Note right of Pub: Commit transaction Note right of Pub: $ cvmfs_server publish loop For each object pack Note right of Pub: Upload object pack Pub ->> GW: POST /api/v1/payloads/<TOKEN> GW ->> Receiver: Stream object pack Note right of Receiver: Deserialize files from object pack loop For each file in object pack Receiver ->> S0: Upload file end end Note right of Pub: Commit lease Pub ->> GW: POST /api/v1/leases/<TOKEN> GW ->> Receiver: Commit Note right of Receiver: Reconcile local and remote changes Note right of Receiver: Create new catalogs up to the repository root Receiver ->> S0: Upload catalogs Note right of Receiver: Sign and upload new manifest Receiver ->> S0: Upload manifest