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yRCA

yRCA enables identifying the possible root causes for a (failure) event to happen in a service instance in a multi-service application, only based on the application logs.

How to Run yRCA

yRCA provides a Python3-based command-line interface, which can be run with the following command:

python3 yrca.py [OPTIONS] EVENT LOGS TEMPLATES

where

  • EVENT is the path to the file containing the logged event that is to be explained (e.g., event-edgeRouter.log),
  • LOGS is the path to the file containing the logged events to be considered for explaining EVENT, viz., for finding the possible failure cascades causing EVENT to happen (e.g., all.log), and
  • TEMPLATES is the path to a YAML file specifying the templates for parsing logged events and assigning them with a type (e.g., chaos-echo.yml)

By default, yRCA finds all possible explanations, viz., the failure cascades that may have possibly caused EVENT to happen. It then returns the possible explanations grouped based on their structure, and it ranks the returned explanation groups based on the frequency with which they occur). yRCA can anyhow be configured with the available CLI OPTIONS, viz.,

  • --help to print a help on the usage of yrca.py,
  • -v or --verbose, to run yRCA in verbose mode (viz., to not group identified explanations but rather return them plain),
  • -n N or --nSols=N, to set the number N of possible explanations to identify, and
  • -r X or --root=X to require X to be the root causing service of identified explanations.

How yRCA Works

yRCA is composed of two main components, viz., the parser and the explainer, which are invoked in sequence by the main module (explain), which implements the command-line interface.

The Parser

The parser provides a function parseEvents for parsing a file applicationLogs, containing events logged by service instances in the considered run of a multi-service application. An example of logged event is the following:

{
  "message":"2021-09-28 14:14:18.796 ERROR 1 --- [p-nio-80-exec-7] d.u.s.chaosecho.EchoServiceController    : Failing to contact frontend (request_id: [712399e1-b5ff-42b7-9a3b-2d9293fbeca7]). Root cause: org.springframework.web.client.HttpServerErrorException$InternalServerError: 500 : [{\"hash\":-1898628045,\"content\":\"Failing to contact backend services\"}]",
  "version":"1.1",
  "severity":"ERROR",
  "source_host":"10.0.0.2",
  "pid":"1",
  "@version":"1",
  "created":"2021-09-28T14:13:23.14966049Z",
  "timestamp":"2021-09-28 14:14:18.796",
  "event":"Failing to contact frontend (request_id: [712399e1-b5ff-42b7-9a3b-2d9293fbeca7]). Root cause: org.springframework.web.client.HttpServerErrorException$InternalServerError: 500 : [{\"hash\":-1898628045,\"content\":\"Failing to contact backend services\"}]",
  "tag":"edgeRouter",
  "container_name":"sockecho_edgeRouter.1.yhoejj5k0f2uc8lzcollgeala",
  "@timestamp":"2021-09-28T14:14:18.796Z",
  "container_id":"737b523ff95e5860eea879cc5bc9bc34d9ac7f11487b797e47f6705ec56e3ed9",
  "class":"d.u.s.chaosecho.EchoServiceController",
  "tags":["spring_boot"]
 }

whose fields severity, container_name, event, message, timestamp, and @timestamp are used by parseEvents to elicit information on the logged event. Based on such information, parseEvents generates a representation of logged events in Prolog, e.g,

log(edgeRouter,sockecho_edgeRouter_1,1632831258.796,timeout(frontend,'712399e1-b5ff-42b7-9a3b-2d9293fbeca7'),'Failing to contact frontend (request_id: [712399e1-b5ff-42b7-9a3b-2d9293fbeca7]). Root cause: org.springframework.web.client.HttpServerErrorException$InternalServerError: 500 : [{"hash":-1898628045,"content":"Failing to contact backend services"}]',err).

and puts it in a given targetFile. The latter can either be the knowledgeBase corresponding to all logged events or the event to be explained.

To enable parsing any type of log file, the parser exploits log templating, viz., it imports a parse function from the templater module. The latter implements all the logic needed to parse log events based on the input TEMPLATES (see above). Example of templates for the Chaos Echo benchmarking application can be found in data/templates.

Other templates can be provided for parsing the logs of other applications, provided that they are given as a YAML file structured as follows:

client_send: [list_of_regex]
client_receive: [list_of_regex]
client_error: [list_of_regex]
client_timeout: [list_of_regex]
server_receive: [list_of_regex]
server_send: [list_of_regex]

The Explainer

The explainer essentially takes the Prolog representation of the input files generated by the parser and runs a Prolog query to identify the desired explanations. The latter is done by running the Prolog program explain.pl, which provides all the rules for identifying the desired amount of explanations for a given event.