1. Metrics data published Via different methods Monitoring Server
Monitored Machine
Agent
Pattern-1
Passive?
Metrics data published
Via different methods
Monitoring Server
Monitored Machine
Agent
request commands to be run on the monitored machine, which return the status of the machine
Bunch of Scripts in Any Language.
Agent will execute those scripts.
Results to central server or to other scripts to take action.
Pattern-2
Active?
Pattern-3:
Hybrid
Monitoring Server
(optional)
(Config/
Command/
Probe)
Metrics
Data
NRPE (Nagios Remote plugin Executor) A Nagios centric protocol to collect remote metrics (active checks).
NSCA (Nagios Service Check Acceptor) Another Nagios centric protocol for submitting results (passive checks).
NRDP A Nagios replacment for NSCA.
check_mk Is a protocol utilized by the check_mk monitoring system.
Syslog A protocol primarily designed for submitting log records to central servers.
Graphite Graphite is a graphing solution which allows you do real-time graphing.
SMTP SMTP is used for sending (this more of a toy currently).
CollectD A protocol for collecting information
REST Web based easily firewalled protocol.
internal mechanisms for checking the status of hosts and services.
Collectd
external programs (called plugins) to do all the dirty work
Icinga, nagios,
Plugins are compiled executables or scripts (Perl scripts, shell scripts, etc.) that can be run from a command line to check the status or a host or service. Icinga uses the results from plugins to determine the current status of hosts and services
Plugins act as an abstraction layer between the monitoring logic present in the Icinga daemon and the actual services and hosts that are being monitored.
Monitored Machine
Agent

2. Pattern-1 Vs Pattern-2 Pattern1 Pattern2
Internal Mechanism for checking the status of the hosts/servers
Not Mandatory to have such built-in mechanism – can rely on external mechanism
No Trigger from the server to begin monitoring
Trigger required from the monitoring server.
Apart from simple thresholds and filters – complex operations are carried out at the monitoring server.
Complex Modifications can happen at the agent before sending the data to the server.
Passive?
active monitoring of systems 

3. Agent and pattern Agent Pattern Collectd 1 Monasca Snap 3*
Node-exporter
Telegraf
Icinga 2
Sensu 3
Diamond
Reimann
Beats
Ceilometer
1|2
Munin
Nagios
Centreon
NSClient++
OpenNMS
Agent and pattern

4. Which is the most common Pattern?
No clear winner!

5. Maximum number of metrics support?
Nagios.
How?
Number of plugins –

6. Which agent supports dynamic configuration?
All Pattern-2 and Pattern-3 agents.
Custom solutions for Pattern-1.

7. Any of the agents been used in large-scale real-world deployments
Any of the agents been used in large-scale real-world deployments? If so, please provide the details on the performance.
Collectd: Many blogs by those who have deployed.
No performance data – rather, minimal.
Part of a complete solution.
Riemann, Telegraf – same problem as collectd.
Nagios:
Many deployments
There are performance issues.

8. Interoperability: Which agent is 'most interoperable'
Interoperability: Which agent is 'most interoperable'? (Work with maximum of 'servers' (collection node)
Collectd
monasca
Prometheus
nagios
sensu
Riemann
Telegraf

9. Which agent provides maximum 'freedom' w. r. t
Which agent provides maximum 'freedom' w.r.t. Licenses (core agent + plugins)?
Sensu, Telegraf, Reimann, Diamond.
MIT license provides the maximum freedom.

10. Best for Time Series Databases – Direct compatibility and Publishes to maximum Databases.
Collectd. Next (Snap)
Influxdb, Elasticsearch, Cassandra, OpenTSDB, Prometheus, Graphite, Riak.
Druid – Missing!!!!
Graphite (store and graph metrics)
Collection, Forwarding, Visualization, Monitoring, Storage-Backends, etc.
Collectd, Reimann, Sensu, Nagios, Icinga, Diamond, Graphite

11. Which agent is part of a solution that has Analytics, Alerts, and Graphing.
Almost all!

12. Which agent has the least - Libraries, OS/Kernel versions, etc.?
Mostly Similar, but Collectd stood out.
Adaptability to the system configuration is also better.
Python based tools.

13. Which solution has “plugins” for “processing” the metrics – and what type?
Soln
Threshold
Statistics
Anomaly Detection
Tagging
Collectd Y N
SNAP N?
Telegraf
Mostly realized by Kapacitor.
Sensu
Monasca
Node Exporter
Ceilometer
Icinga
Nagios & Variants N*
Diamond
Reimann
Beats
Handled by the other Elastic solutions
Munin

14. Gaps: Are there any metrics/Events that are not supported by any of the agent and that are relevant to NFV?
Metrics: NO.
*** When the collection point is guest, there are challenges with those metrics that relies of Virtualization platform to expose access to the hardware (ex: PMU).
Single Solution: NO
Events: NO***
Single Solution: YES (no single solution addresses all the events).
What all sources and references considered:
Barometer project -
OpenStack Monitoring Projects
VNFM Monitoring Solutions.
Vendor Blogs.

15. What all agents support metrics over REST-API.
Collectd
Ceilometer
SNAP
Monasca*
Nagios*, Icinga*
Riemann*

16. Anybody supporting REDFISH APIs?
None.
As Almost all vendors (Dell, HP, SuperMicro, etc) are already providing the support (via built-in controllers, agent-free) for both custom or generic clients.
No need for additional entity between.
Maybe, we can have an entity that gets the metrics via Redfish REST-APIs and share it over the ‘common-channel’ (message queue, tcp socket, etc).