The imageserver daemon serves images and objects for the Dominator system.
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.
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 comand:
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
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.
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.
The imagetool utility may be used to add, delete, get and compare images. It is the most important utility in the Dominator system.