oc-observe man page

oc observe — Observe changes to resources and react to them (experimental)

Synopsis

oc observe [Options]

Description

Observe changes to resources and take action on them

This command assists in building scripted reactions to changes that occur in Kubernetes or OpenShift resources. This is frequently referred to as a 'controller' in Kubernetes and acts to ensure particular conditions are maintained. On startup, observe will list all of the resources of a particular type and execute the provided script on each one. Observe watches the server for changes, and will reexecute the script for each update.

Observe works best for problems of the form "for every resource X, make sure Y is true". Some examples of ways observe can be used include:

· Ensure every namespace has a quota or limit range object

· Ensure every service is registered in DNS by making calls to a DNS API

· Send an email alert whenever a node reports 'NotReady'

· Watch for the 'FailedScheduling' event and write an IRC message

· Dynamically provision persistent volumes when a new PVC is created

· Delete pods that have reached successful completion after a period of time.

The simplest pattern is maintaining an invariant on an object - for instance, "every namespace should have an annotation that indicates its owner". If the object is deleted no reaction is necessary. A variation on that pattern is creating another object: "every namespace should have a quota object based on the resources allowed for an owner".

$ cat set_owner.sh
#!/bin/sh
if [[ "$(oc get namespace "$1" --template='{{ .metadata.annotations.owner }}')" == "" ]]; then
oc annotate namespace "$1" owner=bob
fi

$ oc observe namespaces -- ./set_owner.sh

The set_owner.sh script is invoked with a single argument (the namespace name) for each namespace. This simple script ensures that any user without the "owner" annotation gets one set, but preserves any existing value.

The next common of controller pattern is provisioning - making changes in an external system to match the state of a Kubernetes resource. These scripts need to account for deletions that may take place while the observe command is not running. You can provide the list of known objects via the --names command, which should return a newline-delimited list of names or namespace/name pairs. Your command will be invoked whenever observe checks the latest state on the server - any resources returned by --names that are not found on the server will be passed to your --delete command.

For example, you may wish to ensure that every node that is added to Kubernetes is added to your cluster inventory along with its IP:

$ cat add_to_inventory.sh
#!/bin/sh
echo "$1 $2" >> inventory
sort -u inventory -o inventory

$ cat remove_from_inventory.sh
#!/bin/sh
grep -vE "^$1 " inventory > /tmp/newinventory
mv -f /tmp/newinventory inventory

$ cat known_nodes.sh
#!/bin/sh
touch inventory
cut -f 1-1 -d ' ' inventory

$ oc observe nodes -a '{ .status.addresses[0].address }' \
--names ./known_nodes.sh \
--delete ./remove_from_inventory.sh \
-- ./add_to_inventory.sh

If you stop the observe command and then delete a node, when you launch observe again the contents of inventory will be compared to the list of nodes from the server, and any node in the inventory file that no longer exists will trigger a call to remove_from_inventory.sh with the name of the node.

Important: when handling deletes, the previous state of the object may not be
available and only the name/namespace of the object will be passed to your
--delete command as arguments (all custom arguments are omitted).

More complicated interactions build on the two examples above - your inventory script could make a call to allocate storage on your infrastructure as a service, or register node names in DNS, or set complex firewalls. The more complex your integration, the more important it is to record enough data in the remote system that you can identify when resources on either side are deleted.

Experimental: This command is under active development and may change without notice.

Options

--all-namespaces=false
If present, list the requested object(s) across all projects. Project in current context is ignored.
-a, --argument=""
Template for the arguments to be passed to each command in the format defined by --output.
-d, --delete=""
A command to run when resources are deleted. Specify mulitple times to add arguments.
--exit-after=0
Exit with status code 0 after the provided duration, optional.
--listen-addr=":11251"
The name of an interface to listen on to expose metrics and health checking.
--maximum-errors=20
Exit after this many errors have been detected with. May be set to -1 for no maximum.
--names=""
A command that will list all of the currently known names, optional. Specify multiple times to add arguments. Use to get notifications when objects are deleted.
--no-headers=false
Skip printing information about each event prior to executing the command.
--object-env-var=""
The name of an env var to serialize the object to when calling the command, optional.
--once=false
Exit with a status code 0 after all current objects have been processed.
--output="jsonpath"
Controls the template type used for the --argument flags. Supported values are gotemplate and jsonpath.
--print-metrics-on-exit=false
On exit write all metrics to stdout.
--resync-period=0
When non-zero, periodically reprocess every item from the server as a Sync event. Use to ensure external systems are kept up to date. Requires --names
--retry-count=2
The number of times to retry a failing command before continuing.
--retry-on-exit-code=0
If any command returns this exit code, retry up to --retry-count times.
--strict-templates=false
If true return an error on any field or map key that is not missing in a template.
--type-env-var=""
The name of an env var to set with the type of event received ('Sync', 'Updated', 'Deleted', 'Added') to the reaction command or --delete.

Options Inherited from Parent Commands

--api-version=""
DEPRECATED: The API version to use when talking to the server

--as=""
Username to impersonate for the operation.

--certificate-authority=""
Path to a cert. file for the certificate authority.

--client-certificate=""
Path to a client certificate file for TLS.

--client-key=""
Path to a client key file for TLS.

--cluster=""
The name of the kubeconfig cluster to use

--config=""
Path to the config file to use for CLI requests.

--context=""
The name of the kubeconfig context to use

--google-json-key=""
The Google Cloud Platform Service Account JSON Key to use for authentication.

--insecure-skip-tls-verify=false
If true, the server's certificate will not be checked for validity. This will make your HTTPS connections insecure.

--log-flush-frequency=0
Maximum number of seconds between log flushes

--match-server-version=false
Require server version to match client version

-n, --namespace=""
If present, the namespace scope for this CLI request.

--server=""
The address and port of the Kubernetes API server

--token=""
Bearer token for authentication to the API server.

--user=""
The name of the kubeconfig user to use

Example

# observe changes to services
oc observe services

# observe changes to services, including the clusterIP and invoke a script for each
oc observe services -a '{ .spec.clusterIP }' -- register_dns.sh

See Also

oc(1),

History

June 2016, Ported from the Kubernetes man-doc generator

Referenced By

oc(1).

Openshift CLI User Manuals Openshift June 2016