diff --git a/entity-types/infra-haproxyinstance/definition.yml b/entity-types/infra-haproxyinstance/definition.yml
index dd3bf5bc5..4494e3a8f 100644
--- a/entity-types/infra-haproxyinstance/definition.yml
+++ b/entity-types/infra-haproxyinstance/definition.yml
@@ -34,6 +34,8 @@ synthesis:
       haproxy.addr:
       # HAProxy-specific attributes (natively emitted by haproxyreceiver)
       haproxy.proxy_name:
+      # Relationship join key (label-based); indexed by the HAPROXYINSTANCE candidate.
+      haproxy.deployment.name:
       haproxy.service_name:
       # Environment attributes (from resourcedetection processor)
       os.type:
@@ -86,6 +88,8 @@ synthesis:
       haproxy.addr:
       # HAProxy-specific attributes (natively emitted by haproxyreceiver)
       haproxy.proxy_name:
+      # Relationship join key (label-based); indexed by the HAPROXYINSTANCE candidate.
+      haproxy.deployment.name:
       haproxy.service_name:
       # Environment attributes (from resourcedetection processor)
       os.type:
@@ -138,6 +142,8 @@ synthesis:
         ttl: P1D
       haproxy.addr:
       haproxy.proxy_name:
+      # Relationship join key (label-based); indexed by the HAPROXYINSTANCE candidate.
+      haproxy.deployment.name:
       haproxy.service_name:
       os.type:
       host.id:
@@ -184,6 +190,8 @@ synthesis:
         ttl: P1D
       haproxy.addr:
       haproxy.proxy_name:
+      # Relationship join key (label-based); indexed by the HAPROXYINSTANCE candidate.
+      haproxy.deployment.name:
       haproxy.service_name:
       os.type:
       host.id:
@@ -260,6 +268,8 @@ synthesis:
       haproxy.instance.id:
       haproxy.addr:
       haproxy.proxy_name:
+      # Relationship join key (label-based); indexed by the HAPROXYINSTANCE candidate.
+      haproxy.deployment.name:
       host.name:
         ttl: P1D
       host.id:
@@ -300,6 +310,8 @@ synthesis:
       haproxy.instance.id:
       haproxy.addr:
       haproxy.proxy_name:
+      # Relationship join key (label-based); indexed by the HAPROXYINSTANCE candidate.
+      haproxy.deployment.name:
       host.name:
         ttl: P1D
       host.id:
@@ -327,6 +339,7 @@ goldenTags:
 - host.id
 - host.name
 - haproxy.addr
+- haproxy.deployment.name
 - os.type
 - cloud.provider
 - cloud.region
diff --git a/entity-types/infra-haproxyinstance/tests/Metric.json b/entity-types/infra-haproxyinstance/tests/Metric.json
index ec5b96cdf..731656de3 100644
--- a/entity-types/infra-haproxyinstance/tests/Metric.json
+++ b/entity-types/infra-haproxyinstance/tests/Metric.json
@@ -7,6 +7,7 @@
     "haproxy.addr": "http://127.0.0.1:8404/stats",
     "haproxy.proxy_name": "http_front",
     "haproxy.service_name": "FRONTEND",
+    "haproxy.deployment.name": "haproxy-demo-lb",
     "description": "Number of connections over the last elapsed second (frontend). Corresponds to HAProxy's conn_rate metric.",
     "instrumentation.provider": "opentelemetry",
     "metricName": "haproxy.connections.rate",
diff --git a/relationships/candidates/HAPROXYINSTANCE.stg.yml b/relationships/candidates/HAPROXYINSTANCE.stg.yml
new file mode 100644
index 000000000..1f697941b
--- /dev/null
+++ b/relationships/candidates/HAPROXYINSTANCE.stg.yml
@@ -0,0 +1,19 @@
+category: HAPROXYINSTANCE
+lookups:
+  # Deployment-name lookup — indexes the HAPROXYINSTANCE entity by its
+  # haproxy.deployment.name join tag (label-based / Option 5). Both relationship
+  # directions resolve against this single field; the join value is identical on
+  # the client side (tags.haproxy.deployment.name) and the backend side
+  # (tags.haproxy.upstream.deployment.name).
+  - entityTypes:
+      - domain: INFRA
+        type: HAPROXYINSTANCE
+    tags:
+      matchingMode: ALL
+      predicates:
+        - tagKeys: ["haproxy.deployment.name"]
+          field: deploymentName
+    onMatch:
+      onMultipleMatches: RELATE_ALL
+    onMiss:
+      action: NO_OP
diff --git a/relationships/synthesis/EXT-SERVICE-to-INFRA-HAPROXYINSTANCE.stg.yml b/relationships/synthesis/EXT-SERVICE-to-INFRA-HAPROXYINSTANCE.stg.yml
new file mode 100644
index 000000000..6dff7b3b9
--- /dev/null
+++ b/relationships/synthesis/EXT-SERVICE-to-INFRA-HAPROXYINSTANCE.stg.yml
@@ -0,0 +1,30 @@
+relationships:
+  # OTel client service → HAPROXYINSTANCE (CALLS), label-based.
+  # The client (e.g. haproxy-frontend) declares which HAProxy it calls via
+  #   OTEL_RESOURCE_ATTRIBUTES=tags.haproxy.deployment.name=<name>
+  # Note the key: on HAProxy the *client* carries haproxy.deployment.name
+  - name: otelExtServiceCallsHaproxyInstanceByDeploymentLabelStg
+    version: "1"
+    origins:
+      - OpenTelemetry
+    conditions:
+      - attribute: eventType
+        anyOf: [ "Metric" ]
+      - attribute: newrelic.source
+        anyOf: [ "api.metrics.otlp" ]
+      - attribute: entity.type
+        anyOf: [ "SERVICE" ]
+      - attribute: tags.haproxy.deployment.name
+        present: true
+    relationship:
+      expires: PT75M
+      relationshipType: CALLS
+      source:
+        extractGuid:
+          attribute: entity.guid
+      target:
+        lookupGuid:
+          candidateCategory: HAPROXYINSTANCE
+          fields:
+            - field: deploymentName
+              attribute: tags.haproxy.deployment.name
diff --git a/relationships/synthesis/INFRA-HAPROXYINSTANCE-to-EXT-SERVICE.stg.yml b/relationships/synthesis/INFRA-HAPROXYINSTANCE-to-EXT-SERVICE.stg.yml
new file mode 100644
index 000000000..090d257cc
--- /dev/null
+++ b/relationships/synthesis/INFRA-HAPROXYINSTANCE-to-EXT-SERVICE.stg.yml
@@ -0,0 +1,32 @@
+relationships:
+  # HAPROXYINSTANCE → OTel backend service (CALLS), label-based.
+  # The backend (e.g. haproxy-backend-8001/8002) declares the HAProxy that fronts
+  # it via
+  #   OTEL_RESOURCE_ATTRIBUTES=tags.haproxy.upstream.deployment.name=<name>
+  # ("upstream" = the load balancer in front of the backend). Note the key: on
+  # HAProxy the *backend* carries haproxy.upstream.deployment.name
+  - name: haproxyInstanceCallsOtelExtServiceByUpstreamLabelStg
+    version: "1"
+    origins:
+      - OpenTelemetry
+    conditions:
+      - attribute: eventType
+        anyOf: [ "Metric" ]
+      - attribute: newrelic.source
+        anyOf: [ "api.metrics.otlp" ]
+      - attribute: entity.type
+        anyOf: [ "SERVICE" ]
+      - attribute: tags.haproxy.upstream.deployment.name
+        present: true
+    relationship:
+      expires: PT75M
+      relationshipType: CALLS
+      source:
+        lookupGuid:
+          candidateCategory: HAPROXYINSTANCE
+          fields:
+            - field: deploymentName
+              attribute: tags.haproxy.upstream.deployment.name
+      target:
+        extractGuid:
+          attribute: entity.guid