oracle vm messages

Using the Oracle VM Message API for your own applications...

There are two ways to communicate through the APIs, a quick and easy one and a more comprehensive one.

The quick and easy method of just sending and receiving messages.

Sending messages using ovm_utils or using the Oracle VM CLI to the VM

# ssh admin@localhost -p 10000
admin@localhost's password: 
OVM> sendVmMessage Vm name=ol6u3apitest key=foo message=bar log=no
Command: sendVmMessage Vm name=ol6u3apitest key=foo message=bar log=no
Status: Success
Time: 2012-12-27 09:04:29,890 PST

or

# ./ovm_vmmessage -u admin -p ######## -h localhost -v ol6u3apitest -k foo -V bar
Oracle VM VM Message utility 0.5.2.
Connected.
VM : 'ol6u3apitest' has status :  Running.
Sending message.
Message sent successfully.

so both of the examples send a key/value pair of foo=bar to the VM.

Receiving messages on the VM side using ovmd

Inside the VM, you can use the ovmd executable to retrieve and send messages back.

# ovmd -l 

lists all currently set key/value pairs

# ovmd -g key 

get a value from inside the VM

# ovmd -r key

delete a key out of the current cache

# ovmd -x

delete the key/value values currently set in the cache

so in the case of the message sent through the manager above, you can see it in the VM :

# ovmd -l
{"foo":"bar"}
{"mykey":"myvalue"}

# ovmd -g mykey
myvalue

# ovmd -r mykey
# ovmd -l
{"foo":"bar"}

Setting key/value pairs inside the VM and retrieve through the manager

# ovmd -p key=value

set a key/value pair inside the VM

# ovmd -p newkey=newvalue
# ovmd -l
{"foo":"bar"}
{"newkey":"newvalue"}

use ovm_vmmessage to query the value of a key, use the -q option with the key to query to retrieve a set value.

ovm_vmmessage will also return when this key was set inside the VM.

# ./ovm_vmmessage -u admin -p Manager1 -h localhost -v ol6u3apitest -q newkey
Oracle VM VM Message utility 0.5.2.
Connected.
VM : 'ol6u3apitest' has status :  Running.
Querying for key 'newkey'.
Query successful.
Query for Key : 'newkey' returned value 'newvalue'.
Key set 2 minutes ago.

So with just these simple tools it's possible to set up a model where you send message from your application outside of a VM to the VM through the OVMAPI and also send messages from an application inside a VM back. You can write your own daemon process that runs and queries for values or just do it manually. A recommendation would be to create a naming convention for your product. For instance, for the Oracle VM template configuration we use com.oracle.linux.[values]. You could consider something similar or just have [application].[key] or whatever you want. The maximum size of the total message is 8Kb.

Next up will be extending template config for your own application.