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Last active July 23, 2021 12:21
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Circuit Breaking in HAProxy
backend serviceA
default-server maxconn 30 check observe layer7 error-limit 50 on-error mark-down inter 1s rise 30 slowstart 20s
server s1 192.168.0.10:80
server s2 192.168.0.11:80
backend serviceA
# Create storage for tracking client info
stick-table type string size 1 expire 30s store http_req_rate(10s),gpc0,gpc0_rate(10s),gpc1
# Is the circuit broken?
acl circuit_open be_name,table_gpc1 gt 0
# Reject request if circuit is broken
http-request return status 503 content-type "application/json" string "{ \"message\": \"Circuit Breaker tripped\" }" if circuit_open
# Begin tracking requests
http-request track-sc0 be_name
# Count HTTP 5xx server errors
http-response sc-inc-gpc0(0) if { status ge 500 }
# Store the HTTP request rate and error rate in variables
http-response set-var(res.req_rate) sc_http_req_rate(0)
http-response set-var(res.err_rate) sc_gpc0_rate(0)
# Check if error rate is greater than 50% using some math
http-response sc-inc-gpc1(0) if { int(100),mul(res.err_rate),div(res.req_rate) gt 50 }
server s1 192.168.0.10:80 check
server s2 192.168.0.11:80 check
stick-table type string size 1 expire 30s store http_req_rate(10s),gpc0,gpc0_rate(10s),gpc1
acl circuit_open be_name,table_gpc1 gt 0
http-request return status 503 content-type "application/json" string "{ \"message\": \"Circuit Breaker tripped\" }" if circuit_open
http-request track-sc0 be_name
http-response sc-inc-gpc0(0) if { status ge 500 }
http-response set-var(res.req_rate) sc_http_req_rate(0)
http-response set-var(res.err_rate) sc_gpc0_rate(0)
http-response sc-inc-gpc1(0) if { int(100),mul(res.err_rate),div(res.req_rate) gt 50 }
http-response sc-inc-gpc1(0) if { var(res.req_rate) gt 100 } { int(100),mul(res.err_rate),div(res.req_rate) gt 50 }
backend serviceA
default-server maxconn 30 check observe layer7 error-limit 50 on-error mark-down inter 1s rise 30 slowstart 20s
# Circuit break the whole backend if the number
# of servers becomes less than or equal to 4
http-request return status 503 content-type "application/json" string "{ \"message\": \"Circuit Breaker tripped\" }" if { nbsrv() le 4 }
server s1 192.168.0.10:80
server s2 192.168.0.11:80
server s3 192.168.0.12:80
server s4 192.168.0.13:80
server s5 192.168.0.14:80
server s6 192.168.0.15:80
server s7 192.168.0.16:80
server s8 192.168.0.17:80
server s9 192.168.0.18:80
server s10 192.168.0.19:80
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