imageserver

The imageserver daemon serves images and objects for the Dominator system.

Status page

The imageserver provides a web interface on port 6971 which provides a status page, links to built-in dashboards and access to performance metrics and logs. If imageserver is running on host myhost then the URL of the main status page is http://myhost:6971/. An RPC over HTTP interface is also provided over the same port.

Startup

Imageserver is started at boot time, usually by one of the provided init scripts. The imageserver process is baby-sat by the init script; if the process dies the init script will re-start it. It may be stopped with the command:

service imageserver stop

which also kills the baby-sitting init script. It may be started with the command:

service imageserver start

There are many command-line flags which may change the behaviour of imageserver but many have defaults which should be adequate for most deployments. Built-in help is available with the command:

imageserver -h

Key configuration parameters

The init script reads configuration parameters from the /etc/default/imageserver file. The following is the minimum likely set of parameters that will need to be configured.

If ARCHIVE_MODE is set to true then the imageserver will ignore all delete operations, effectively turning it into an archiver (backup).

The IMAGE_DIR variable specifies the directory where images are stored. It is recommended to specify a directory on a file-system with plenty of free space.

The IMAGE_SERVER_HOSTNAME variable specifies another imageserver which will serve as the source of image updates. This may be used to configure simple, fast and secure image replication between imageservers. If this variable is unset then the imageserver is a master/standalone server

The OBJECT_DIR variable specifies the directory where objects are stored. It is recommended to specify a directory on a file-system with plenty of free space.

The USERNAME variable specifies the username that imageserver should run as. Since imageserver does not need root privileges, the init script runs imageserver as this user.

Security

RPC access is restricted using TLS client authentication. Imageserver expects a root certificate in the file /etc/ssl/CA.pem which it trusts to sign certificates which grant access. It also requires a certificate and key which grant it the ability to get images and objects from another imageserver. These should be in the files /etc/ssl/imageserver/cert.pem and /etc/ssl/imageserver/key.pem, respectively.

Control

The imagetool utility may be used to add, delete, get and compare images. It is the most important utility in the Dominator system.