This section provides technical details on the CernVM-FS server setup including the infrastructure necessary for an individual repository. It is highly recommended to first consult ":ref:`sct_serveranatomy`" for a more general overview of the involved directory structure.
A CernVM-FS server installation depends on the following environment setup and tools to be in place:
- Appropriate kernel version. You must have ONE of the following:
- kernel 4.2.x or later.
- RHEL7.3 kernel (for OverlayFS)
- Backend storage location available through HTTP
- Backend storage accessible at
/srv/cvmfs/...(unless stored on S3) - cvmfs and cvmfs-server packages installed
CernVM-FS stores the entire repository content (file content and
metadata catalogs) into a content addressable storage (CAS). This
storage can either be a file system at /srv/cvmfs or an S3
compatible object storage system (see ":ref:`sct_s3storagesetup`" for
details). In the former case the contents of /srv/cvmfs are as
follows:
| File Path | Description |
|---|---|
/srv/cvmfs |
Central repository storage location Can be mounted or symlinked to another location before creating the first repository. |
/srv/cvmfs/<fqrn> |
Storage location of a specific repository Can be symlinked to another location before creating the repository <fqrn>. This location
needs to be both writable by the repository owner
and accessible through an HTTP server. |
/srv/cvmfs/<fqrn>/.cvmfspublished |
Manifest file of the repository The manifest provides the entry point into the repository. It is the only file that needs to be signed by the repository's private key. |
/srv/cvmfs/<fqrn>/.cvmfswhitelist |
List of trusted repository certificates Contains a list of certificate fingerprints that should be allowed to sign a repository manifest (see .cvmfspublished). The whitelist needs to be signed by a globally trusted private key. |
/srv/cvmfs/<fqrn>/data |
CAS location of the repository Data storage of the repository. Contains catalogs, files, file chunks, certificates and history databases in a content addressable file format. This directory and all its contents need to be writable by the repository owner. |
/srv/cvmfs/<fqrn>/data/00..ff |
Second CAS level directories Splits the flat CAS namespace into multiple directories. First two digits of the file content hash defines the directory the remainder is used as file name inside the corresponding directory. |
/srv/cvmfs/<fqrn>/data/txn |
CAS transaction directory Stores partial files during creation. Once writing has completed, the file is committed into the CAS using an atomic rename operation. |
The spool area of a repository contains transaction infrastructure and
scratch area of a Stratum0 or specifically a release manager machine
installation. It is always located inside /var/spool/cvmfs with
directories for individual repositories. Note that the data volume of
the spool area can grow very large for massive repository updates since
it contains the writable union file system branch and a CernVM-FS client
cache directory.
| File Path | Description |
|---|---|
/var/spool/cvmfs |
CernVM-FS server spool area Contains administrative and scratch space for CernVM-FS repositories. This directory should only contain directories corresponding to individual CernVM-FS repositories. |
/var/spool/cvmfs/<fqrn> |
Individual repository spool area Contains the spool area of an individual repository and might temporarily contain large data volumes during massive repository updates. This location can be mounted or symlinked to other locations. Furthermore it must be writable by the repository owner. |
/var/spool/cvmfs/<fqrn>/cache |
CernVM-FS client cache directory Contains the cache of the CernVM-FS client mounting the r/o branch (i.e. /var/spool/cvmfs/<fqrn>/rdonly) of the
union file system mount point located at
/cvmfs/<fqrn>.
The content of this directory is fully managed
by the CernVM-FS client and hence must be
configured as a CernVM-FS cache and writable for
the repository owner. |
/var/spool/cvmfs/<fqrn>/rdonly |
CernVM-FS client mount point Serves as the mount point of the CernVM-FS client exposing the latest published state of the CernVM-FS repository. It needs to be owned by the repository owner and should be empty if CernVM-FS is not mounted to it. |
/var/spool/cvmfs/<fqrn>/scratch |
Writable union file system scratch area All file system changes applied to /cvmfs/<fqrn> during a transaction will be
stored in this directory. Hence, it potentially
needs to accommodate a large data volume
during massive repository updates. Furthermore
it needs to be writable by the repository
owner. |
/var/spool/cvmfs/<fqrn>/tmp |
Temporary scratch location Some CernVM-FS server operations like publishing store temporary data files here, hence it needs to be writable by the repository owner. If the repository is idle this directory should be empty. |
/var/spool/cvmfs/<fqrn>/client.config |
CernVM-FS client configuration This contains client configuration variables for the CernVM-FS client mounted to /var/spool/cvmfs/<fqrn>/rdonly. Most notibly
it needs to contain CVMFS_ROOT_HASH
configured to the latest revision published in
the corresponding repository. This file needs to
be writable by the repository owner. |
The authoritative configuration of a CernVM-FS repository is located in
/etc/cvmfs/repositories.d and should only be writable by the
administrator. Furthermore, the repository's keychain is located in
/etc/cvmfs/keys and follows the naming convention <fqrn>.crt for
the certificate, <fqrn>.key for the repository's private key and
<fqrn>.pub for the public key. All of those files can be symlinked
somewhere else if necessary.
| File Path | Description |
|---|---|
/etc/cvmfs/repositories.d |
CernVM-FS server config directory This contains the configuration directories for individual CernVM-FS repositories. Note that this path is shortened using /.../repos.d/ in the
rest of this table. |
/.../repos.d/<fqrn> |
Config directory for specific repo This contains the configuration files for one specific CernVM-FS repository server. |
/.../repos.d/<fqrn>/server.conf |
Server configuration file Authoriative configuration file for the CernVM-FS server tools. This file should only contain :ref:`valid server configuration variables <apxsct_serverparameters>` as it controls the behaviour of the CernVM-FS server operations like publishing, pulling and so forth. |
/.../repos.d/<fqrn>/client.conf |
Client configuration file Authoriative configuration file for the CernVM-FS client used to mount the latest revision of a Stratum 0 release manager machine. This file should only contain :ref:`valid client configuration variables <apxsct_clientparameters>`. This file must not exist for Stratum 1 repositories. |
/.../repos.d/<fqrn>/replica.conf |
Replication configuration file Contains configuration variables for Stratum 1 specific repositories. This file must not exist for Stratum 0 repositories. |
Apart from file and directory locations a CernVM-FS server installation
depends on a few environment configurations. Most notably the
possibility to access the backend storage through HTTP and to allow for
mounting of both the CernVM-FS client at
/var/spool/cvmfs/<fqrn>/rdonly and a union file system on /cvmfs/<fqrn>.
Granting HTTP access can happen in various ways and depends on the chosen backend storage type. For an S3 hosted backend storage, the CernVM-FS client can usually be directly pointed to the S3 bucket used for storage (see ":ref:`sct_s3storagesetup`" for details). In case of a local file system backend any web server can be used for this purpose. By default, CernVM-FS assumes Apache and uses that automatically.
Internally the CernVM-FS server uses a SUID binary (i.e.
cvmfs_suid_helper) to manipulate its mount points. This is necessary
since transactional CernVM-FS commands must be accessible to the
repository owner that is usually different from root. Both the mount
directives for /var/spool/cvmfs/<fqrn>/rdonly and /cvmfs/<fqrn>
must be placed into /etc/fstab for this reason. By default,
CernVM-FS uses the following entries for these mount points:
cvmfs2#<fqrn> /var/spool/cvmfs/<fqrn>/rdonly fuse \ allow_other,config=/etc/cvmfs/repositories.d/<fqrn>/client.conf: \ /var/spool/cvmfs/<fqrn>/client.local,cvmfs_suid 0 0 aufs_<fqrn> /cvmfs/<fqrn> aufs br=/var/spool/cvmfs/<fqrn>/scratch=rw: \ /var/spool/cvmfs/<fqrn>/rdonly=rr,udba=none,ro 0 0