Beware the trailing slash in Proxy balancer
ProxyPass / balancer://app <Proxy balancer://app> BalancerMember http://10.0.0.166:8181 BalancerMember http://10.0.0.166:8182 BalancerMember http://10.0.0.166:8183 BalancerMember http://10.0.0.166:8184 BalancerMember http://10.0.0.166:8185 BalancerMember http://10.0.0.166:8186 BalancerMember http://10.0.0.166:8187 BalancerMember http://10.0.0.166:8188 BalancerMember http://10.0.0.166:8189 BalancerMember http://10.0.0.166:8190 Proxy>
This is not
ProxyPass / balancer://app <Proxy balancer://app> BalancerMember http://10.0.0.166:8181/ BalancerMember http://10.0.0.166:8182/ BalancerMember http://10.0.0.166:8183/ BalancerMember http://10.0.0.166:8184/ BalancerMember http://10.0.0.166:8185/ BalancerMember http://10.0.0.166:8186/ BalancerMember http://10.0.0.166:8187/ BalancerMember http://10.0.0.166:8188/ BalancerMember http://10.0.0.166:8189/ BalancerMember http://10.0.0.166:8190/ Proxy>
This is also not correct
ProxyPass / balancer://app/ <Proxy balancer://app/> BalancerMember http://10.0.0.166:8181/ BalancerMember http://10.0.0.166:8182/ BalancerMember http://10.0.0.166:8183/ BalancerMember http://10.0.0.166:8184/ BalancerMember http://10.0.0.166:8185/ Proxy>