Latency is increased when Envoy is attached to the Elasticsearch Coordinate node

I'm stuck in the latency issue with Envoy when it is applied to our service.

Here is a simple architecture.
AS-IS: Client <-> ALB:TargetGroup(port:1111) <-> Coordinate (ES)
TO-BE: Client <-> ALB:TargetGroup(port:2222) <-> Envoy <-> Coordinate (ES)

Envoy is running on the same instance with Coordinate as a sidecar.

Envoy has a duration log in access log and I couldn't find timeout or latency increased from there. Thus, it seems Envoy itself doesn't make any latency issue. But, also I couldn't find latency increment from ALB TargetGroup response time metric.

Also, I've tried below but same result.

1. dns_refresh_rate: 3600000
2. remove lua filter
3. generate_request_id: false
4. circuit_breakers: thresholds: - priority: "DEFAULT" max_connections: 2147483647 max_requests: 2147483647 max_pending_requests: 2147483647

ALB response time metric (left: TOBE , right: ASIS):

envoy.yaml:

!ignore dynamic_sockets:
  - &admin_address { address: 0.0.0.0, protocol: TCP, port_value: 9901 }
  - &elasticsearch_proxy_address { address: 0.0.0.0, protocol: TCP, port_value: 9100 }
  # Use 'address: host.docker.internal' for local test
  - &elasticsearch_address { address: 127.0.0.1, protocol: TCP, port_value: 9200 }


admin:
  address:
    socket_address: *admin_address

# The static_resources contain everything that is configured
# statically when Envoy starts, as opposed to dynamically at runtime.
static_resources:
  listeners:
    - name: elasticsearch_proxy
      address:
        socket_address: *elasticsearch_proxy_address
      filter_chains:
        - filters:
            - name: envoy.filters.network.http_connection_manager
              typed_config:
                "@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
                stat_prefix: ingress_http
                request_timeout: 2s
                generate_request_id: false
                access_log:
                  - name: envoy.access_loggers.file
                    typed_config:
                      "@type": type.googleapis.com/envoy.extensions.access_loggers.file.v3.FileAccessLog
                      path: /services/logs/envoy/access.log
                      log_format:
                        # https://www.envoyproxy.io/docs/envoy/latest/configuration/observability/access_log/usage
                        json_format:
                          authority: "%REQ(:AUTHORITY)%"
                          req_method: "%REQ(:METHOD)%"
                          req_path: "%REQ(X-ENVOY-ORIGINAL-PATH?:PATH)%"
                          req_body: "%DYNAMIC_METADATA(envoy.filters.http.lua:request.info:request_body)%"
                          downstream_addr: "%DOWNSTREAM_REMOTE_ADDRESS%"
                          start_time: "%START_TIME%"
                          bytes_sent: "%BYTES_SENT%"
                          res_code: "%RESPONSE_CODE%"
                          elapsed: "%DURATION%"
                route_config:
                  name: local_router
                  virtual_hosts:
                    - name: local
                      domains: [ "*" ]
                      routes:
                        - match: { prefix: "/" }
                          route:
                            cluster: elasticsearch
                http_filters:
                  - name: envoy.filters.http.lua
                    typed_config:
                      "@type": type.googleapis.com/envoy.extensions.filters.http.lua.v3.Lua
                      inline_code: |
                        local filter = require "lib.filter"
                        function envoy_on_request(request_handle)
                          filter.handle_request(request_handle)
                        end
                  - name: envoy.filters.http.router

  clusters:
    - name: elasticsearch
      connect_timeout: 2s
      type: STRICT_DNS
      lb_policy: ROUND_ROBIN
      dns_lookup_family: V4_ONLY
      circuit_breakers:
        thresholds:
        - priority: "DEFAULT"
          max_connections: 2147483647
          max_requests: 2147483647
          max_pending_requests: 2147483647
      load_assignment:
        cluster_name: elasticsearch
        endpoints:
          - lb_endpoints:
              - endpoint:
                  address:
                    socket_address: *elasticsearch_address

lua.filter

M = {}

-- Stream handle API of Lua HTTP filter
-- @doc https://www.envoyproxy.io/docs/envoy/v1.7.0/configuration/http_filters/lua_filter#config-http-filters-lua-stream-handle-api
function M.handle_request(request)
    local t = {}
    for chunk in request:bodyChunks() do
        local len = chunk:length()
        local str = chunk:getBytes(0, len)
        str = str:gsub('\n', '')
        str = str:gsub('%s', '')
        table.insert(t, str)
    end

    local request_body = table.concat(t, '')
    -- https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_filters/lua_filter#dynamic-metadata-object-api
    request:streamInfo():dynamicMetadata():set("envoy.filters.http.lua",
            "request.info", { request_body = request_body }
    )
end

return M

What else I can do to find the root cause of latency increment?