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Problem Statment

Currently, on EVE software module, ZedAgent is responsible for top level orchestration, basos upgrade validation, cloud connectivity for configuration/status.

In the whole EVE node boot up process, ZedAgent and associated modules are spawned, only after network connectivity(through nim, waitfor address) and device registration (zedclient).

For  baseos upgrade validation, this leaves a gap between node boot up and real baseos upgrade transition process invocation in zedagent. Any failure inbetween, the device boot up until zedagent starts, may lead to device being struck in some indefinite state and may turn the device to a non-functional unit. 


Proposal

The zedagent module will be broken-up. The baseos upgrade validation and and device health will be managed by DevAgent. The DevAgent will be one of the first modules to be spawned along with ledmanager, and will be persistent for the whole lifetime of the EVE node. The ZedAgent will be only responsible for cloud connectivity and configuration parsing and status/metrics publication. Baseosmgr will interact with devagent for the baseos upgrade  installation and valitaion.

EVE Node Health Monitor Function

EVE Node health check functionality, currently consists of the following, 

 Watchdog Time : For Pillar Agent(s) Health and responsiveness.

 Each agent's health is monitored through software watchdog. If an agent does not retouch the pid file for watchdog time interval, the device is rebooted.

Reset Time: For controller connectivity health in normal operation mode

On controller connectivity loss, the EVE node is rebooted after the reset time interval.

 Fallback Time: For controller connectivity health during baseos upgrade validation

For controller connectivity loss, EVE Node reboots and falls back to fallback image, after the fallback time interval.

Current Implementation

The watchdog time handler functionality is based on hardware watchdog(wdctl), and it is part of device-steps.sh.

The reset and fallback time functionalities are currently part of ZedAgent Module.  

Refactoring Details

The watchdog time functionality will remain as such. The reset and fallback time functionality will be moved into a new agent called, devagent. The whole baseos upgrade validation orchestration functionality will be moved into devagent module. Devagent will be spwaned along with ledmanager. Devagent will listen to ledmanager ledblinker config messages to determine controller connectivity status along with successful configuration pull message time stamps from zedagent, to orchestrate the baseos upgrade validation functionality. Devagent will be owner for Zboot config and will publish them for usage by baseosmanager. Also on successful baseos installation and reset/fallback timer expiry, the device reboot operations will be triggered through "devagent status"  pusub topic.

Zedagent module will only be responsible for controller connectivity related functionalities, like pulling latest configuration blob from controller, and publishing status/info/metrics  messages to controller. And will update this information through "zedagent status" pubsub topic. Zedagent will subscribe to "devagent status" pubsub topic to execute device reboot commands.

Baseosmanger will listen to devagent module, zboot config messages to handle, and update zboot status, for baseos installation and upgrade validation orchestration.

In a nutshell, the following are going to be changes in event handling per module.

Baseosmgr Module

Baseosmgr wiill subscribe to the following topic,

  •       "zboot config" from devagent

            For baaseos installation and upgrade validation

ZedAgent Module

 Zedagent wiill subscribe to the following topic,

  •      "devagent status" , generated by devagent

           For executing device reboot command

           To publish the remaining test time to controller, for baseos upgrade validation

  Zedagent will publish the following topic,

  •        "zedagent status"

           Time stamp for last successful configuration pull from controller

DevAgent Module

DevAgent  module will  subscribe to the following topics,

  •    "ledBlinker config", generated by zedclient/zedagent, etc

For EVE node registration, controller connectivity change events

  •    "zboot status", generated by baseosmgr

        For baseos installation and upgrade validation orchestration

  •    "zedagent status", generated by zedagent

        For the last successful config fetch time stamp, from controller

DevAgent will publish the following topics,

  •     "zboot config"

        Zboot partition information

  •     "devagent status"

         For device reboot event, in baseos installation and reset/fallback timer expiry 

         Remaining test time, for publication  to controller ( consumed by zedagent)


P.S.

For completeness and future workscope, the following items are noted, for EVE node health. This list is not exhaustive, and the necessary actions for them needs be defined. 

  • cpu usage health
  • disk space usage health
  • network usage health
  • each agent's basic functionality check, (on upgrade)
  • controller driven testing and marking the baseos as active


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