consul/connect: default envoy concurrency to 1

Previously, every Envoy Connect sidecar would spawn as many worker
threads as logical CPU cores. That is Envoy's default behavior when
`--concurrency` is not explicitly set. Nomad now sets the concurrency
flag to 1, which is sensible for the default cpu = 250 Mhz resources
allocated for sidecar proxies. The concurrency value can be configured
in Client configuration by setting `meta.connect.proxy_concurrency`.

Closes #9341

CHANGELOG.md

@@ -30,6 +30,7 @@ IMPROVEMENTS:
  * consul: Support Consul namespace (Consul Enterprise) in client configuration. [[GH-8849](https://github.com/hashicorp/nomad/pull/8849)]
  * consul/connect: Dynamically select envoy sidecar at runtime [[GH-8945](https://github.com/hashicorp/nomad/pull/8945)]
  * consul/connect: Enable setting `datacenter` field on connect upstreams [[GH-8964](https://github.com/hashicorp/nomad/issues/8964)]
+ * consul/connect: Envoy concurrency now defaults to 1 rather than number of cores [[GH-9341](https://github.com/hashicorp/nomad/issues/9341)]
  * csi: Support `nomad volume detach` with previously garbage-collected nodes. [[GH-9057](https://github.com/hashicorp/nomad/issues/9057)]
  * csi: Relaxed validation requirements when checking volume capabilities with controller plugins, to accommodate existing plugin behaviors. [[GH-9049](https://github.com/hashicorp/nomad/issues/9049)]
  * driver/docker: Upgrade pause container and detect architecture [[GH-8957](https://github.com/hashicorp/nomad/pull/8957)]

client/client.go

@@ -98,17 +98,26 @@ const (
 	allocSyncRetryIntv = 5 * time.Second
 
 	// defaultConnectSidecarImage is the image set in the node meta by default
-	// to be used by Consul Connect sidecar tasks
-	// Update sidecar_task.html when updating this.
+	// to be used by Consul Connect sidecar tasks. As of Nomad 1.0, this value
+	// is only used as a fallback when the version of Consul does not yet support
+	// dynamic envoy versions.
 	defaultConnectSidecarImage = "envoyproxy/envoy:v1.11.2@sha256:a7769160c9c1a55bb8d07a3b71ce5d64f72b1f665f10d81aa1581bc3cf850d09"
 
 	// defaultConnectGatewayImage is the image set in the node meta by default
-	// to be used by Consul Connect Gateway tasks.
+	// to be used by Consul Connect Gateway tasks. As of Nomad 1.0, this value
+	// is only used as a fallback when the version of Consul does not yet support
+	// dynamic envoy versions.
 	defaultConnectGatewayImage = defaultConnectSidecarImage
 
 	// defaultConnectLogLevel is the log level set in the node meta by default
-	// to be used by Consul Connect sidecar tasks
+	// to be used by Consul Connect sidecar tasks.
 	defaultConnectLogLevel = "info"
+
+	// defaultConnectProxyConcurrency is the default number of worker threads the
+	// connect sidecar should be configured to use.
+	//
+	// https://www.envoyproxy.io/docs/envoy/latest/operations/cli#cmdoption-concurrency
+	defaultConnectProxyConcurrency = "1"
 )
 
 var (
@@ -1403,6 +1412,9 @@ func (c *Client) setupNode() error {
 	if _, ok := node.Meta["connect.log_level"]; !ok {
 		node.Meta["connect.log_level"] = defaultConnectLogLevel
 	}
+	if _, ok := node.Meta["connect.proxy_concurrency"]; !ok {
+		node.Meta["connect.proxy_concurrency"] = defaultConnectProxyConcurrency
+	}
 
 	return nil
 }

nomad/job_endpoint_hook_connect.go

@@ -28,6 +28,7 @@ var (
 			"args": []interface{}{
 				"-c", structs.EnvoyBootstrapPath,
 				"-l", "${meta.connect.log_level}",
+				"--concurrency", "${meta.connect.proxy_concurrency}",
 				"--disable-hot-restart",
 			},
 		}

website/pages/docs/job-specification/sidecar_task.mdx

@@ -61,49 +61,54 @@ group service has a [`sidecar_service`][sidecar_service] stanza.
 The default sidecar task is equivalent to:
 
 ```hcl
-   sidecar_task {
-     name   = "connect-proxy-<service>"
+sidecar_task {
+  name = "connect-proxy-<service>"
 
-     lifecycle {
-       hook = "prestart"
-       sidecar = true
-     }
+  lifecycle {
+    hook    = "prestart"
+    sidecar = true
+  }
 
-     driver = "docker"
-     config {
-       image = "${meta.connect.sidecar_image}"
-       args  = [
-         "-c",
-         "${NOMAD_SECRETS_DIR}/envoy_bootstrap.json",
-         "-l",
-         "${meta.connect.log_level}"
-       ]
-     }
+  driver = "docker"
+  config {
+    image = "${meta.connect.sidecar_image}"
+    args = [
+      "-c",
+      "${NOMAD_SECRETS_DIR}/envoy_bootstrap.json",
+      "-l",
+      "${meta.connect.log_level}",
+      "--concurrency",
+      "${meta.connect.proxy_concurrency}",
+      "--disable-hot-restart"
+    ]
+  }
 
-     logs {
-       max_files     = 2
-       max_file_size = 2 # MB
-     }
+  logs {
+    max_files     = 2
+    max_file_size = 2 # MB
+  }
 
-     resources {
-       cpu    = 250 # MHz
-       memory = 128 # MB
-     }
+  resources {
+    cpu    = 250 # MHz
+    memory = 128 # MB
+  }
 
-     shutdown_delay = "5s"
-   }
+  shutdown_delay = "5s"
+}
 ```
 
-The `meta.connect.sidecar_image` and `meta.connect.log_level` are [_client_
+The `meta.connect.sidecar_image`, `meta.connect.log_level`, and
+`meta.connect.proxy_concurrency` variables are [_client_
 configurable][nodemeta] variables with the following defaults:
 
 - `sidecar_image` - `(string: "envoyproxy/envoy:v${NOMAD_envoy_version}")` - The official
    upstream Envoy Docker image, where `${NOMAD_envoy_version}` is resolved automatically
    by a query to Consul.
 - `log_level` - `(string: "info")` - Envoy sidecar log level. "`debug`" is useful for
   debugging Connect related issues.
+- `proxy_concurrency` - `(string: "1")` - The number of [worker threads][worker_threads] the Envoy
+  sidecar will run.
 
-`meta.connect.sidecar_image` can be configured at the job, group, or task level.
 Custom images can make use of Consul's preferred Envoy version by making use of
 Nomad's version interpolation, e.g.
 
@@ -169,3 +174,4 @@ The following example configures resources for the sidecar task and other config
 [resources]: /docs/job-specification/resources 'Nomad resources Job Specification'
 [logs]: /docs/job-specification/logs 'Nomad logs Job Specification'
 [nodemeta]: /docs/configuration/client#meta
+[worker_threads]: https://www.envoyproxy.io/docs/envoy/latest/operations/cli#cmdoption-concurrency

website/pages/docs/upgrade/upgrade-specific.mdx

@@ -19,7 +19,7 @@ standard upgrade flow.
 
 ### HCL2 for Job specification
 
-Nomad 1.0.0 adopts HCL2 for parsing the job spec. HCL2 extends HCL with more
+Nomad v1.0.0 adopts HCL2 for parsing the job spec. HCL2 extends HCL with more
 expression and reuse support, but adds some stricter schema for HCL blocks (a.k.a. stanzas).  Check [HCL](/docs/job-specification/hcl2) for more details.
 
 ### Signal used when stopping Docker tasks
@@ -73,12 +73,12 @@ Nomad. The specific configuration values replaced are:
 
 ### Envoy proxy versions
 
-Nomad 1.0.0 changes the behavior around the selection of Envoy version used
+Nomad v1.0.0 changes the behavior around the selection of Envoy version used
 for Connect sidecar proxies. Previously, Nomad always defaulted to Envoy v1.11.2
 if neither the `meta.connect.sidecar_image` parameter or `sidecar_task` stanza
 were explicitly configured. Likewise the same version of Envoy would be used for
 Connect ingress gateways if `meta.connect.gateway_image` was unset. Starting with
-Nomad 1.0.0, each Nomad Client will query Consul for a list of supported Envoy
+Nomad v1.0.0, each Nomad Client will query Consul for a list of supported Envoy
 versions. Nomad will make use of the latest version of Envoy supported by the
 Consul agent when launching Envoy as a Connect sidecar proxy. If the version of
 the Consul agent is older than v1.7.8, v1.8.4, or v1.9.0, Nomad will fallback to
@@ -94,6 +94,15 @@ the time of the upgrade for each node will ensure Connect workloads are properly
 rescheduled onto nodes in such a way that the Nomad Clients, Consul agents, and
 Envoy sidecar tasks maintain compatibility with one another.
 
+### Envoy worker threads
+
+Nomad v1.0.0 changes the default behaviour around the number of worker threads
+created by the Envoy sidecar proxy when using Consul Connect. Previously, the
+Envoy [`--concurrency`][envoy_concurrency] argument was left unset, which caused
+Envoy to spawn as many worker threads as logical cores available on the CPU. The
+`--concurrency` value now defaults to `1` and can be configured by setting the
+[`meta.connect.proxy_concurrency`][proxy_concurrency] property in client configuration.
+
 ## Nomad 0.12.8
 
 ### Docker volume mounts
@@ -859,6 +868,7 @@ deleted and then Nomad 0.3.0 can be launched.
 [drain-api]: /api-docs/nodes#drain-node
 [drain-cli]: /docs/commands/node/drain
 [dst]: /docs/job-specification/periodic#daylight-saving-time
+[envoy_concurrency]: https://www.envoyproxy.io/docs/envoy/latest/operations/cli#cmdoption-concurrency
 [gh-6787]: https://github.com/hashicorp/nomad/issues/6787
 [gh-8457]: https://github.com/hashicorp/nomad/issues/8457
 [gh-9148]: https://github.com/hashicorp/nomad/issues/9148
@@ -870,6 +880,7 @@ deleted and then Nomad 0.3.0 can be launched.
 [plugins]: /docs/drivers/external
 [preemption-api]: /api-docs/operator#update-scheduler-configuration
 [preemption]: /docs/internals/scheduling/preemption
+[proxy_concurrency]: /docs/job-specification/sidecar_task#proxy_concurrency
 [reserved]: /docs/configuration/client#reserved-parameters
 [task-config]: /docs/job-specification/task#config
 [tls-guide]: https://learn.hashicorp.com/tutorials/nomad/security-enable-tls