Session Group Monitor

BACKEND SCRIPT

Monitor flow based metrics stream. When new flows are created, terminated, timeout, new activity is seen on flows, etc. You can also control which flows get flushed to the Trisul-Hub database.

Structure

Table sg_monitor

The Lua table sg_monitor = {..} can contain one or more of the following handler functions.

field type when called
session_guid String (optional) Session group id. The default is {99A78737-4B41-4387-8F31-8077DB917336} for IPv4/IPv6 flows
onnewflow Function( Engine, flow) A new flow was seen. The Flow contains details of the flow
onupdate Function( Engine, flow) Some metrics were update in the flow object. This can be called as much as every second per flow.
onterminate Function( Engine, flow) Flow terminated
onbeginflush Function( Engine, ts) Before starting to flush all metrics to db
flushfilter Function( Engine, flow) Before flushing each flow. Return true if you want to save flow in DB, return false to skip this flow
onflush Function( Engine, flow) Called for each flow as they are being flushed
onendflush Function( Engine) After all flows have been flushed for this interval
onmetronome Function( Engine, timestamp, tick_count, tick_interval) called every second ( Tick Interval)

Objects Reference

Flow

Represents a flow and all its metrics. Note that you can access the f:flow() object which gives you access to the tuples like source_ip, destination_ip, ports, etc.

field return type description
key string A unique string identifying the flow. Same as flow():id() below
flow FlowID a FlowID object representing the flow tuples like source_ip, port, destination_ip, port etc
time_window number,number start and last activity time seconds (a tv_sec Unix epoch time) of the flow. starttm,lasttm = flow:time_window().
state flow state The state of the flow, whether it is timeout, RST, FIN, or closed normally.
az_bytes number number of bytes in a→z direction. the A-side can be obtained from session:flow():ipa_readable()
za_bytes bytes seen in z→a direction
az_packets number number packets seen in a→z direction
za_packets number number packets seen in z→a direction
az_payload_bytes number a→z payload bytes does not include the network headers, only the TCP payload
za_payload_bytes number z→a payload bytes does not include the network headers, only the TCP payload
tags string a pipe separated string of all tags attached to the flow
add_tag Example flow:add_tag("suspect") allows you to add a tag to the set of tags already there
setup_rtt number For TCP flows only – Round Trip Time in microseconds as measured by the TCP handshake
retransmissions number Number of retransmitted sequence numbers observed, total of both directions

Session state

The state field from the above object contains an OR of the following enums

SESS_INIT 0×0001 all connections have this bit
SESS_SEEN_SYN 0×0002 seen a SYN (of the 3-way handshake)
SESS_SEEN_SYN_ACK 0×0004 seen a SYN_ACK
SESS_SEEN_SYN_ACK_ACK 0×0008 seen ACK of the SYN-ACK the handshake
SESS_A_END_SERVER 0×0010 The A-Endpoint identified by flow is the destination. The Trisul formula is to place the lower numbered port endpoint as the Z-End. Using this information you can identify the client and server of the flow based on the actual SYN packet
SESS_Z_END_SERVER 0×0020 The Z-Endpoint is the server. This is the normal situation
SESS_SEEN_FIN 0×0040 Seen a FIN close
SESS_SEEN_RST 0×0080 Seen a RST close
SESS_TIMEDOUT 0×0100 Flow timed out, could indicate packet loss or other issue
SESS_ERROR 0×0200 Some other unknown error with flow caused it to flush
SESS_INCOMPLETE 0×0400 One of the two directions did not close properly
SESS_TERMINATED 0×0800 Proper termination

Example use of object

The following example prints the IP address of endpoints and total bytes



  onnewflow = function(engine, newflow)
    local flow_object = newflow:flow()

    print("ip a-end"..flow_object:ipa_readable())
    print("ip z-end"..flow_object:ipz_readable())
    print("total bytes"..newflow:az_bytes()+newflow:za_bytes())

    ..

  end,

Functions Reference

Function onnewflow

Purpose

Use this to collect flow based metrics.

When called

When a new flow is detected. A new flow is detected when a metric for a new flow key is updated and that flow key is not currently being tracked in the streaming backend.

Parameters

engine An Engine object use this object to add metrics, resources, or alerts into the Trisul framework
flow A Flow object the flow

Return value

Ignored

Example


Function onupdate

High frequency function
For busy networks this can result in thousands of updates every second. Keep your LUA function onupdate(..) efficient and avoid I/O or blocking.

Purpose

Used to track all streaming metrics assigned to a flow.

When called

This is called when any event or metric is detected on a flow.

Parameters

engine An Engine object use this object to add metrics, resources, or alerts into the Trisul framework
flow A Flow object the flow

Return value

Ignored

Example


Function onterminate

Purpose

When a flow is terminated. The termination can be a normal TCP termination or a timeout.

When called

When a normal TCP flow termination is detected or when the flow is timedout from the streaming data structures.

Parameters

engine An Engine object use this object to add metrics, resources, or alerts into the Trisul framework
flow A Flow object the flow

Return value

Ignored

Example


Function onbeginflush

Purpose

Use this to setup your code to handle the start of flows being flushed to the backend storage.

When called

When accumulated streaming metrics for all flows are about to be flushed to the backend.

Parameters

engine An Engine object use this object to add metrics, resources, or alerts into the Trisul framework
timestamp A timestamp (tv_sec) value timestamp value – number of seconds since Jan 1 1970

Return value

Ignored

Example


Function onflush

Purpose

Process each flow as they are flushed.

When called

Just before each flow is flushed to the backend database. At this point all the metrics are attached to the flow and ready for consumption.

Parameters

engine An Engine object use this object to add metrics, resources, or alerts into the Trisul framework
flow A Flow object the flow

Return value

Ignored

Example


Function flushfilter

Purpose

Control if a flow is flushed to the database backend or not.

When called

Just before each flow is flushed to the database. You can look at the contents of the flow object and determine if you want this flow to be flushed or not.

Parameters

engine An Engine object use this object to add metrics, resources, or alerts into the Trisul framework
flow A Flow object the flow

Return value

true
flush this flow to the backend database node
false
dont flush this flow

Voting considerations

If you have multiple scripts S1, S2, .. SN each voting differently on flushfilter(), the following rule is enforced.

  1. ALL scripts have to vote NO to flush by returning false.
  2. Even if one script Sx returns YES or does not implement flushfilter(), the artifact is flushed.

Example


Function onendflush

Purpose

End of a flush cycle.

When called

When all the flows are flushed for this cycle. You can clean up here what you initalized in onbeginflush

Parameters

engine An Engine object use this object to add metrics, resources, or alerts into the Trisul framework

Return value

Ignored

Example


Function onmetronome

Purpose

Plug into a metronome.

When called

If you define a onmetronome(..) function you will be plugged into the Trisul metronome heartbeat mechanism. This method will be called every metronome tick(roughly every second). The context in which this method is called is threadsafe and you can add metrics to the Engine from here.

Parameters

engine An Engine object use this object to add metrics, resources, or alerts into the Trisul framework
timestamp Number Current timestamp (tv_sec epoch seconds)
tick_count Number An incremeting tick counter
tick_interval Number The tick interval, in seconds.

Return value

Ignored

Example