Feature pages are design documents that developers have created while collaborating on oVirt.

Most of them areoutdated, but provide historical design context.

They arenotuser documentation and should not be treated as such.

Documentation is available here.

Detailed Host PM Proxy Preferences

Host Power Management Proxy Preferences

Summary

When Power Management is defined on the Host and the host becomes non-responding , the engine will attempt to restart the Host after a graceful period is passed The Host non-responding treatment is doing the following actions Send a Stop command

    Wait for status 'off' 
      (controlled by FenceStopStatusDelayBetweenRetriesInSec,FenceStopStatusRetries configuration values)
    Send a Start command
    Wait for status 'on' 
      (controlled by FenceStartStatusDelayBetweenRetriesInSec,FenceStartStatusRetries configuration values)

The current implementation of PM proxy selection is based on selection of host from the data center with ‘UP’ status. This implementation is not robust enough, since fence action such as ‘RestartVds’ which is comprised of two fence actions (stop & start) might be able to complete the first action, but fails to detect a proxy for the second. In some cases the entire DC becomes non-responsive or even stopped. In that case no host on DC could act as a proxy.

This document describes an extension to the current proxy selection algorithm that enables each Host to define its proxy chain as a priority list.

Specifically, the local host may be chosen as a proxy for fencing operations This may be achieved by installing a full VDSM packages on the local machine by using Local VDSM

An alternative to installing a lightweight local VDSM is writing a Fence Wrapper

And finally , we can also implement it by additional VDSM Instance

Owner

  • Feature owner: Eli Mesika (emesika)

    • GUI Component owner: Eli Mesika (emesika)

    • REST Component owner: Eli Mesika (emesika)

    • Engine Component owner: Eli Mesika (emesika)

    • QA Owner: Yaniv Kaul (ykaul)

  • Email: emesika@redhat.com

Current status

  • Target Release: 3.2
  • Status: Design
  • Last updated date: Nov 4 2012

Detailed Description

CRUD

Adding a pm_proxy_preferences column to vds_static table. this column represents a comma separated proxy preferences lists per Host The default value for this column will be : ‘CLUSTER,DC’ So, if this value is for example the default value, a Host that is in non-responsive state and has Power Management configured will be fenced using the first UP Host in Cluster then the first UP Host in the Data Center then the engine.

Modify views vds and vds_with_tags to include pm_proxy_preferences Update InsertVdsStatic and UpdateVdsStatic SPs to handle pm_proxy_preferences

DAO

Adding handling of pm_proxy_preferences to VdsStaticDAODbFacadeImpl VdsDAODbFacadeImpl

Metadata

Adding test for the new pm_proxy_preferences field in VdsStaticDAOTest Adding test data in fixtures.xml

Configuration

A new configuration value will be added named FenceProxyDefaultPreferences The default value will be : CLUSTER,DC

This configuration value should be exposed to the engine-config tool.

Business Logic

Add pmProxyPreferences field to VdsStatic Add pmProxyPreferences field to VDS Allow to edit the PmProxyPreferences property FencingExecutor::FindVdsToFence Modify the following commands to send the value of proxy preferences settings for the Host: AddVdsCommand UpdateVdsCommand


Apply the logic of searching for the proxy according to the pmProxyPreferences value

Flow

Start/Stop commands are passed to the Host fencing agent via a proxy machine, in this case The pm_proxy_preferences of the Host that is in non-responding state is examined for each entry in the comma-separated values for this field we are trying to send the fencing command (Start/Stop) via the proxy In the case that the proxy is the local engine , a validation phase of checking existence of local installed fence-agents package is issued The first proxy on the pm_proxy_preferences chain that succeeded to execute the command takes If all proxies in the pm_proxy_preferences chain fails to execute the fencing operation , an ERROR is written to the log. Actual proxy used in a fencing operation should be logged as well.

API

The REST API will be enhanced to include the new Proxy Preferences as follows

   `    ` `       ` `          ` `             ``cluster` `          ` `         ` `             ``dc` `          ` `       ` `    ` ` `

To achieve that we should do the following: in api.xsd (schema) define new elements: PmProxy which contains one field : predefined

    `*`PmProxies`*` which contains a list of PmProxy

Add enum PmProxyType {CLUSTER,DATACENTER} in org.ovirt.engine.api.model package Add PmProxyType enum to capabilities (BackendCapabilitiesResource) Add enum validations Add custom mapping for these new power-management fields in HostMapper.java, for both REST–>Backend and Backend–>REST directions) Add metadata to rsdl_metadata_v-3.1.yaml

User Experience

A new list will be added to the Power Management Tab when adding a new Host or modifying existing Host The list will have by default the entries : CLUSTER ,DC and ENGINE(in 3.2) The user may also use the UP and DOWN buttons to change items order inside the list(item order = priority) See pre-defined values for details.

Installation/Upgrade

Add the new pm_proxy_preferences column in the upgrade script. Adding configuration values as described in Configuration

User work-flows

Enforcement

Affected oVirt projects

Host Power Management Multiple Agents

Documentation / External references

Features/HostPMProxyPreferences

Future Directions

The user may add other existing Host by pressing the ADD button, this will open a drop-down list of all available Hosts defined in the Data Center except the currently edited/added Host We are skipping that for the first phase since it has complexities when a Host is removed or moved to another Cluster etc.

oVirt 3.5

This RFEis planned for oVirt 3.5 We will address for 3.5 only the option to look for proxy outside the DC where the host is located and try to use other DCs This will be done by adding to the pm_proxy_preferences field which is defaulted now to “cluster,DC” another option named other_dc. (The pm_proxy_preferences value is available via the UI Host New/Edit PM TAB in the field named “source” , in the API it is under ) Example of POST request to update Host pm proxy details :

   `    ` `       ` `          ` `              ``cluster` `           ` `          ` `              ``dc` `           ` `          ` `              ``other_dc` `           ` `      ` `    ` `  `

The default will stay “cluster,DC” and the admin can change this value per host using the API

Open Issues

pre-defined values

Are pre-defined values applied implicitly? Meaning, if a user modified the PM Proxy Preferences to be for example only : IP1,IP2 Does this means that this is the actual chain and if both IP1 & IP2 fails to serve as proxies the Power Management operation fails? or, we should say that this actually implies IP1,IP2,engine,cluster,dc implicitly? In case of that, what should we apply if user set PM Proxy Preferences to be engine,IP1,IP2 ? Suggestion: engine,cluster,dc should be applied implicitly and missing definitions from the original default (engine,cluster.dc) will be applied using the same priority Examples: engine,IP1,IP2 => engine,IP1,IP2,cluster,dc IP1,dc,IP2 => IP1,dc,IP2,engine,cluster

Local VDSM

In the case that engine is selected as a proxy, we may want a separate service (temporary name : local vdsm) that will run on the local host and expose only the fencing functionality from VDSM This option has major affect on the effort/cost and time-line of this feature since we need to write a new service for that, package it , install it etc.

Fence Wrapper

A script or standalone program that will call the fence-agents package scripts directly An option is to use the separation of fenceAgent.py from API.py as suggested here (Invocation in this case from JNA ) In this case we do not need a Local VDSM

VDSM Instance

A separate instance of vdsm, listening on a separate port.

JNA

Java Native Access provides Java programs easy access to native shared libraries without using the Java Native Interface.

Example: The following program loads the local C standard library implementation and uses it to call the printf function.

  import com.sun.jna.Library;
  import com.sun.jna.Native;
  import com.sun.jna.Platform;
  /** Simple example of native library declaration and usage. */
  public class HelloWorld {
     public interface CLibrary extends Library {
         CLibrary INSTANCE = (CLibrary) Native.loadLibrary(
             (Platform.isWindows() ? "msvcrt" : "c"), CLibrary.class);
         void printf(String format, Object... args);
     }
     public static void main(String[] args) {
         CLibrary.INSTANCE.printf("Hello, World\n");
         for (int i = 0; i < args.length; i++) {
             CLibrary.INSTANCE.printf("Argument %d: %s\n", i, args[i]);
         }
     }
  }

Category: Feature