[THREESCALE-9537] Configure batcher policy storage

CHANGELOG.md

@@ -55,6 +55,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Added `APICAST_CLIENT_REQUEST_HEADER_BUFFERS` variable to allow configure of the NGINX `client_request_header_buffers` directive: [PR #1446](https://github.com/3scale/APIcast/pull/1446), [THREESCALE-10164](https://issues.redhat.com/browse/THREESCALE-10164)
 
+- Added the `APICAST_POLICY_BATCHER_SHARED_MEMORY_SIZE` variable to allow configuration of the batcher policy's share memory size. [PR #1452](https://github.com/3scale/APIcast/pull/1452), [THREESCALE-9537](https://issues.redhat.com/browse/THREESCALE-9537)
+
 ## [3.14.0] 2023-07-25
 
 ### Fixed

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. The accepted [size units](https://github.com/openresty/lua-nginx-module?tab=readme-ov-file#lua_shared_dict) are k and m.
+
 ### `OPENTELEMETRY`
 
 This environment variable enables NGINX instrumentation using OpenTelemetry tracing library.

gateway/conf.d/backend.conf

@@ -21,3 +21,15 @@ location /transactions/oauth_authrep.xml {
 
   echo "transactions oauth_authrep!";
 }
+
+location /transactions/authorize.xml {
+  access_by_lua_block {
+    local delay = tonumber(ngx.var.arg_delay) or 0
+
+    if delay > 0 then
+      ngx.sleep(delay)
+    end
+  }
+
+  echo "transactions authorize!";
+}

gateway/conf/nginx.conf.liquid

@@ -94,15 +94,6 @@ http {
     {% include file %}
   {% endfor %}
 
-  lua_shared_dict limiter 1m;
-
-  # This shared dictionaries are only used in the 3scale batcher policy.
-  # 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_locks 1m;
-
   {% for file in "sites.d/*.conf" | filesystem %}
     {% include file %}
   {% endfor %}

gateway/http.d/shdict.conf

@@ -2,3 +2,11 @@ lua_shared_dict api_keys 30m;
 lua_shared_dict rate_limit_headers 20m;
 lua_shared_dict configuration 10m;
 lua_shared_dict locks 1m;
+lua_shared_dict limiter 1m;
+
+# This shared dictionaries are only used in the 3scale batcher policy.
+# These requirements will remain in place until we allow policy to
+# modify this template.
+lua_shared_dict cached_auths 20m;
+lua_shared_dict batched_reports {{env.APICAST_POLICY_BATCHER_SHARED_MEMORY_SIZE | default: "20m"}};
+lua_shared_dict batched_reports_locks 1m;

gateway/src/apicast/policy/3scale_batcher/3scale_batcher.lua

@@ -127,20 +127,12 @@
   cache_handler(cache, key, { status = backend_status })
 end
 
-local function handle_backend_ok(self, transaction, cache_handler)
-  if cache_handler then
-    update_downtime_cache(self.backend_downtime_cache, transaction, 200, cache_handler)
-  end
-
+local function handle_backend_ok(self, transaction)
   self.auths_cache:set(transaction, 200)
   self.reports_batcher:add(transaction)
 end
 
-local function handle_backend_denied(self, service, transaction, status, headers, cache_handler)
-  if cache_handler then
-    update_downtime_cache(self.backend_downtime_cache, transaction, status, cache_handler)
-  end
-
+local function handle_backend_denied(self, service, transaction, status, headers)
   local rejection_reason = rejection_reason_from_headers(headers)
   self.auths_cache:set(transaction, status, rejection_reason)
   return error(service, rejection_reason)
@@ -182,7 +174,7 @@
 -- might want to introduce a mechanism to avoid this and reduce the number of
 -- calls to backend.
 function _M:access(context)
-  local backend = backend_client:new(context.service, http_ng_resty)
+  local backend = assert(backend_client:new(context.service, http_ng_resty), 'missing backend')
   local usage = context.usage or {}
   local service = context.service
   local service_id = service.id
@@ -216,17 +208,20 @@
     local formatted_usage = usage:format()
     local backend_res = backend:authorize(formatted_usage, credentials)
     context:publish_backend_auth(backend_res)
-    local backend_status = backend_res.status
+    local backend_status = backend_res and backend_res.status
     local cache_handler = context.cache_handler -- Set by Caching policy
     -- this is needed, because in allow mode, the status maybe is always 200, so
     -- Request need to go to the Upstream API
-    update_downtime_cache(self.backend_downtime_cache, transaction, backend_status, cache_handler)
+    if cache_handler then
+      update_downtime_cache(
+        self.backend_downtime_cache, transaction, backend_status, cache_handler)
+    end
 
     if backend_status == 200 then
-      handle_backend_ok(self, transaction, cache_handler)
+      handle_backend_ok(self, transaction)
     elseif backend_status >= 400 and backend_status < 500 then
       handle_backend_denied(
-        self, service, transaction, backend_status, backend_res.headers, cache_handler)
+        self, service, transaction, backend_status, backend_res.headers)
     else
       handle_backend_error(self, service, transaction, cache_handler)
     end

gateway/src/apicast/policy/3scale_batcher/README.md

@@ -63,3 +63,29 @@ The effectiveness of this policy will depend on the cache hit ratio. For use
 cases where the variety of services, apps, metrics, etc. is relatively low,
 caching and batching will be very effective and will increase the throughput of
 the system significantly.
+
+### How many key/value pairs can be contained in 20m of shared memory.
+
+On my Linux x86_64 system `1m` can hold `4033 key/value pairs` with 64-byte keys and
+15-byte values. Changing the size of the shared storage to 10m gives `40673 key/value pairs`.
+It's a linear growth as expected.
+
+The following table shows the number of key/value pairs for different storage size:
+
+| Shared storage size | Key length | Value length | Key/value pairs |
+| ---- | ---- | ---- | ---- |
+| 10m | 64 | 15 | 40672 |
+|  | 128 | 15 | 40672 |
+|  | 256 | 15 | 20336 |
+|  | 512 | 15 | 10168 |
+| 20m | 64 | 15 | 81408 |
+|  | 128 | 15 | 81408 |
+|  | 256 | 15 | 40704 |
+|  | 512 | 15 | 20352 |
+| 40m | 64 | 15 | 162848 |
+|  | 128 | 15 | 162848 |
+|  | 256 | 15 | 81424 |
+|  | 512 | 15 | 40712 |
+
+In practice, the actual number will depend on the size of the key/value pair, the
+underlying operating system (OS) architecture and memory segment sizes, etc... More details [here](https://blog.openresty.com/en/nginx-shm-frag/)