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Making Images

A collection of recipes to make images. These assume you have generated image content by some means. See the guide on manifest-driven image building for how to build image content easily and quickly.

I just want to push a few files to my machines

You can do this with a sparse image. Unlike regular images where files on the machines may be removed if they are not in the image, with sparse images only the files present in the image are pushed to the machines. All other files are left alone.

I don't want to restart any services. Just push the files

In this case, you don't provide a triggers file. Normally, triggers are used to tell the Dominator that the specified services should be restarted when certain files are changed.

First, you will need to add your image to the imageserver. Run this command:

imagetool -imageServerHostname=imageserver.my.domain add sparse.0 path "" ""

This will package up the files in the directory tree path and will upload them to the imageserver imageserver.my.domain, creating the image sparse.0. If path is a tarfile (extension .tar) or a compressed tarfile (extension .tar.gz), then the contents of the tarfile are uploaded.

Show me what I just created

You can see the new image in the list of images using the following command:

imagetool -imageServerHostname=imageserver.my.domain list

You can show the contents of the image (the SHA-512 hashes of regular files are shown) using the following command:

imagetool -imageServerHostname=imageserver.my.domain show sparse.0

My image looks good. I'm ready to push it

All you need to do is decide which machine(s) you want to push the new image to and edit the MDB (Machine Data Base) records for those machines. For each machine record, you need to create/update the RequiredImage field with the name of your new image (sparse.0 in this example). Shortly afterwards the Dominator will pick up the updated MDB data and will push the new image to the appropriate machines. If machines are down, they will be automatically updated once they are back online. Your work is done.

I changed my mind. I want to restart a service

Imagine that your sparse image has the SSH daemon configuration file: /etc/ssh/sshd.conf and you want to restart sshd if the file changes. You will need to create a file with the following content:

[
    {
        "MatchLines": [
            "/etc/ssh/sshd[.]conf",
            "/usr/sbin/sshd"
        ],
        "Service": "sshd"
    }
]

This says that whenever the /etc/ssh/sshd.conf or /usr/sbin/sshd files are changed (note the regular expression syntax), the sshd service should be restarted (normally the command service sshd stop; service sshd start commands are executed). If this triggers configuration is stored in the file /tmp/triggers.sshd then you could use the following command to create the image, this time with the triggers configuration:

imagetool -imageServerHostname=imageserver.my.domain add sparse.0 path "" /tmp/triggers.sshd

I've realised I want total Domination

You've discovered how powerful it is to push a few files to your machines and have them constantly kept in compliance without having to do further work, and now you want to control the whole root file-systems of your machines. For this you will need to create normal images rather than sparse images. With normal images you will need to specify a filter. This tells the Dominator that certain files should not be updated. For example, you probably don't want to be updating the /etc/fstab or /etc/hostname files, since they will be different on each machine.

A filter file is a simple text file with a list of filter lines, each being a regular expression pathname that you want to exclude from changes. An example filter file may contain:

/etc/fstab
/etc/hostname
/tmp/.*
/var/log/.*
/var/mail/.*
/var/spool/.*
/var/tmp/.*

If this is contained in the file /tmp/filter then you would use the following command to create an image:

imagetool -imageServerHostname=imageserver.my.domain add image.0 path /tmp/filter /tmp/triggers

The main difference between this command and the one shown earlier is that /tmp/filter is passed for the name of the filter file rather than an empty string.

This will package up the files in the directory tree path and will upload them to the imageserver imageserver.my.domain, creating the image image.0. If path is a tarfile (extension .tar) or a compressed tarfile (extension .tar.gz), then the contents of the tarfile are uploaded.