Baselines

Baselines are an optional feature of Configuration Management that allow you to define a set of attributes that all instances of a configuration item (CI) should have. A baseline is a template CI that defines the expected or authorized attributes of a CI. Typically, a baseline only describes the attributes that you expect CIs to share in common and does not include attributes that you expect to vary. For example, a baseline describing PCs might require that all PC CIs be assigned the same model number and operating system version but not the same owner or serial number. In this example, the model number and the operating system would be authorized attributes of the baseline, while the owner and the serial number would be individually-managed attributes.

Baseline records are separate from the CI records they manage. You must first create a baseline record before you can associate it with one or more CIs. All baseline records must have a name, a list of authorized attributes, and a state. Baseline records can optionally have a version number, which administrators can configure from the Configuration Management environment record. A baseline record’s status determines whether you can add or edit attributes, and whether you can associate CIs to the baseline. After you authorize a baseline record, its attributes are locked and you can only associate or remove CIs from the baseline.

It is up to a Configuration Management manager to determine whether a CI that is out of compliance with its baseline is acceptable or requires a change. Keep in mind that both the CI record and the baseline record describe the expected or managed state of a CI. A baseline record is intended to describe the expected state across many similar items. A CI record describes the expected state of an individual item.

There may be cases where it is acceptable for an individual CI to have a different managed state than other CIs in the same baseline. For example, you might have a baseline requiring that all application servers have 8 GB of RAM. However, you may also want one of your application servers, the Web server, to have 16 GB of RAM. You may want to authorize this exception to the baseline rather than creating a new baseline record to describe just one CI.

Baselines only check for compliance against the managed state of the CI. The actual state of the CI is irrelevant to a baseline compliance check. Continuing the example above, the Web server CI record might list 16 GB of RAM as the managed state. This makes it out of compliance with the baseline that requires all application servers to have 8 GB of RAM. If a discovery process later reveals that the Web server actually only has 12 GB of RAM, this might cause Service Manager to open an unplanned change, but it will not cause a new violation of the baseline. Only differences between the CI’s managed state (16 GB of RAM) and the baseline (8 GB of RAM) matter.