How Jelastic "internal" load balancer check nodes health? -


as far understand, jelastic utilizes kind of load balancer deployed behind nodes. if have 2 nodes , 1 node down, how load balancer act? i'm thinking blue-green deployment without traffic distributor add-on.

by default, incoming traffic @ jelastic platform routed between containers via shared load balancer. herewith, node performs constant servers’ health checkups, utilizing nginx upstream check module following settings that:

interval=15000 rise=2 fall=3 timeout=2000 default_down=false;

in such way, containers considered “up” startup, whilst system verifies availability each 15 seconds. if no response received container within 2 seconds, such checkup regarded failed. 3 consecutive fails mark node “down”, whilst 2 successful checks in row - “up”.

as traffic distribution within separate environment, dedicated load balancer node automatically added topology when number of application server instances set more 1 (i.e. it’s scaled out horizontally). jelastic paas provides 4 load balancer stacks can choose between, each of has health check configuration specifics:

nginx - runs simple tcp check (i.e. verifies required server port availability) right before routing user request it; if check fails, next node within layer tried

haproxy - performs regular tcp checks (every 2 seconds default), storing results in table of backends state , keeping up-to-date

apache balancer - no implemented health check procedure default

varnish - backends assigned probe = { .url = "/"; .timeout = 30s; .interval = 60s; .window = 5; .threshold = 2; } parameter within balancer configs, health checks performed once per minute 30 seconds timeout (see official documentation more information)

obviously, default health check settings can manually adjusted needs (through either jelastic file manager gui or via ssh) according appropriate load balancer stack specification - refer official nginx, haproxy, apache balancer or varnish documentation see details on possible settings.


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