Description:
Hippodamia 0.4.2
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
License
For personal and professional use. You cannot resell or redistribute these repositories in their original state.
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