[batcher] Introduce APICAST_POLICY_BATCHER_SHARED_MEMORY_SIZE env var…

…iable

In some cases, the batcher policy will run out of storage space (batched_reports)
and cause metrics to not being reported. This commit adds a new environment
variable to configure the shared memory storage size

doc/parameters.md

@@ -517,6 +517,13 @@ Sets the maximum number and size of buffers used for reading large client reques
 The format for this value is defined by the [`large_client_header_buffers` NGINX
 directive](https://nginx.org/en/docs/http/ngx_http_core_module.html#large_client_header_buffers)
 
+### `APICAST_POLICY_BATCHER_SHARED_MEMORY_SIZE`
+
+**Default:** 20m
+**Value:** string
+
+Sets the maximum size of shared memory used by batcher policy.
+
 ### `OPENTELEMETRY`
 
 This environment variable enables NGINX instrumentation using OpenTelemetry tracing library.

gateway/http.d/shdict.conf

@@ -8,5 +8,5 @@ lua_shared_dict limiter 1m;
 # This is not ideal, but they'll need to be here until we allow policies to
 # modify this template.
 lua_shared_dict cached_auths 20m;
-lua_shared_dict batched_reports 20m;
+lua_shared_dict batched_reports {{env.APICAST_POLICY_BATCHER_SHARED_MEMORY_SIZE | default: "20m"}};
 lua_shared_dict batched_reports_locks 1m;