In the Operator Lifecycle Manager (OLM) ecosystem, the following resources are used to resolve Operator installations and upgrades:
Operator metadata, defined in CSVs, can be stored in a collection called a catalog source. OLM uses catalog sources, which use the Operator Registry API, to query for available Operators as well as upgrades for installed Operators.
Within a catalog source, Operators are organized into packages and streams of updates called channels, which should be a familiar update pattern from OpenShift Container Platform or other software on a continuous release cycle like web browsers.
A user indicates a particular package and channel in a particular catalog source in a subscription, for example an
etcd package and its
alpha channel. If a subscription is made to a package that has not yet been installed in the namespace, the latest Operator for that package is installed.
OLM deliberately avoids version comparisons, so the "latest" or "newest" Operator available from a given catalog → channel → package path does not necessarily need to be the highest version number. It should be thought of more as the head reference of a channel, similar to a Git repository.
Each CSV has a
replaces parameter that indicates which Operator it replaces. This builds a graph of CSVs that can be queried by OLM, and updates can be shared between channels. Channels can be thought of as entry points into the graph of updates:
packageName: example channels: - name: alpha currentCSV: example.v0.1.2 - name: beta currentCSV: example.v0.1.3 defaultChannel: alpha
For OLM to successfully query for updates, given a catalog source, package, channel, and CSV, a catalog must be able to return, unambiguously and deterministically, a single CSV that
replaces the input CSV.
For an example upgrade scenario, consider an installed Operator corresponding to CSV version
0.1.1. OLM queries the catalog source and detects an upgrade in the subscribed channel with new CSV version
0.1.3 that replaces an older but not-installed CSV version
0.1.2, which in turn replaces the older and installed CSV version
OLM walks back from the channel head to previous versions via the
replaces field specified in the CSVs to determine the upgrade path
0.1.1; the direction of the arrow indicates that the former replaces the latter. OLM upgrades the Operator one version at the time until it reaches the channel head.
For this given scenario, OLM installs Operator version
0.1.2 to replace the existing Operator version
0.1.1. Then, it installs Operator version
0.1.3 to replace the previously installed Operator version
0.1.2. At this point, the installed operator version
0.1.3 matches the channel head and the upgrade is completed.
The basic path for upgrades in OLM is:
A catalog source is updated with one or more updates to an Operator.
OLM traverses every version of the Operator until reaching the latest version the catalog source contains.
However, sometimes this is not a safe operation to perform. There will be cases where a published version of an Operator should never be installed on a cluster if it has not already, for example because a version introduces a serious vulnerability.
In those cases, OLM must consider two cluster states and provide an update graph that supports both:
The "bad" intermediate Operator has been seen by the cluster and installed.
The "bad" intermediate Operator has not yet been installed onto the cluster.
By shipping a new catalog and adding a skipped release, OLM is ensured that it can always get a single unique update regardless of the cluster state and whether it has seen the bad update yet.