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Hippodamia observe the state of all registered microservices (aka watch dog).
Pelops Overview
Hippodamia is part of the collection of mqtt based microservices pelops. An overview on the microservice architecture and examples can be found at (http://gitlab.com/pelops/pelops).
for Developers
States of a Microservice
AState Diagram
initialize phase - an onboarding request has been received by the system. if the source has been identified as a known microservice, the existing state will be used, a new one will be initialized.
onboarding - a microserivce has been identified/initialized and the system waits for it to react to the onboarding request response.
active - the observed microservice has been successfully onboarded and sends state updates regularly.
inactive - the microservice has not sent any update for a predefined period.
terminated - the microservice has either send a good-by-message or been inactive for to long.
end state - the system has terminated observation of this microservice.
States of the Corresponding Agent
uninitialized - agent has just started or a restart has been forced. on entry of this state a new uuid will be generated.
initizalized - agent is ready to start onboarding procedure.
onboading - agent has sent an onboarding request and is waiting for an reply
active - agent is constantly sending ping, runtime, and config messages
terminating - agent sends an termination message to the service before shutdown
Topics
see AsyncAPI.
Incoming
contact - for onboarding/offboarding requests
state.ping - listens for new ping messages
state.runtime - listens for new runtime messages
state.config - listens for new config messages
state.end - listens for termination messages ### Outgoing
uuid - individual topic opened by each microservice for the onboarding process
command.ping - request ping messages
command.runtime - request runtime messages
command.config - request config messages
command.onboarding - request re-onboarding
Messages
see AsyncAPI.
Incoming
onboarding request - onboarding request from a microservice
ping - minimum “sign of life” of a microservice
runtime info - ping plus additional runtime information
config state - ping plus service configuration
termination info - end service signal. sent either upon stop of service or as last will via mqtt server.
Outgoing
onboarding response - onboarding response sent by hippodamia to the microservice via the provide onboarding topic from the microservice
re-onboard request - request plus optionally gid
request ping - request plus optionally gid
request runtime info - request plus optionally gid
request full state - request plus optionally gid
Onboarding Sequence
Sequence
First, the microservice subscribes to a unique topic. This topic is sent together with additional information to identify the microservice (especially to look if this microservices has been onboarded previously) to hippodamias onboarding channel. Hippodamia answers with the onboarding response message which primarily contains the gid - the identifier of this particular microservice instance that ideally should be the same even after the n-th onboarding cycle. The repsonse message is published to the unique topic from the microservice. Once the microservice has received its gid, the uniqued topic can be unsubscribed and the reqular topics will be used for further communication.
Ping Sequence
Ping
Ping messages are normally sent by the microservice at arbitrary times. Usually a sent interval of e.g. 60 seconds is implemented. The other possibility is that hippodamia requests a ping message from all onboarded microservices. The same sequence applies to runtime, config and onboarding.
Database
Hippodamia stores all info immediately into the database. * Microservice state * Received messages
1 maintainer
Metadata
1 maintainer
Release files for Hippodamia 0.4.2
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Release files / Hippodamia-0.4.2.tar.gz
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