[Metrics] Use multi-process prometheus in v1 (vllm-project#503)

* Enable multi-process prometheus in v1

Signed-off-by: Shaoting Feng <shaotingf@uchicago.edu>

* Make PROMETHEUS_MULTIPROC_DIR selectable

Signed-off-by: Shaoting Feng <shaotingf@uchicago.edu>

* Use type string

Signed-off-by: Shaoting Feng <shaotingf@uchicago.edu>

---------

Signed-off-by: Shaoting Feng <shaotingf@uchicago.edu>

Author: Shaoting-Feng

helm/templates/deployment-vllm-multi.yaml

@@ -183,6 +183,11 @@ spec:
           - name: LMCACHE_LOG_LEVEL
             value: "DEBUG"
           {{- if hasKey . "v1" }}
+          {{- if eq ($modelSpec.vllmConfig.v1 | toString) "1" }}
+          {{- $dir := default "/tmp" $modelSpec.vllmConfig.prometheusMultiprocDir }}
+          - name: PROMETHEUS_MULTIPROC_DIR
+            value: {{ $dir | quote }}
+          {{- end }}
           - name: VLLM_USE_V1
             value: {{ $modelSpec.vllmConfig.v1 | quote }}
           {{- else }}