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03-features.md

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Features
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routing-release
gorouter

Features

Dynamic Routing Table

Gorouters routing table is updated dynamically via the NATS message bus. NATS can be deployed via BOSH with (cf-deployment) or standalone using nats-release.

To add or remove a record from the routing table, a NATS client must send register or unregister messages. Records in the routing table have a maximum TTL of 120 seconds, so clients must heartbeat registration messages periodically; we recommend every 20s. Route Registrar is a BOSH job that comes with Routing Release that automates this process.

When deployed with Cloud Foundry, registration of routes for apps pushed to CF occurs automatically without user involvement. For details, see [Routes and Domains] (https://docs.cloudfoundry.org/devguide/deploy-apps/routes-domains.html).

Registering Routes via NATS

When the gorouter starts, it sends a router.start message to NATS. This message contains an interval that other components should then send router.register on, minimumRegisterIntervalInSeconds. It is recommended that clients should send router.register messages on this interval. This minimumRegisterIntervalInSeconds value is configured through the start_response_delay_interval configuration property. Gorouter will prune routes that it considers to be stale based upon a separate "staleness" value, droplet_stale_threshold, which defaults to 120 seconds. Gorouter will check if routes have become stale on an interval defined by prune_stale_droplets_interval, which defaults to 30 seconds. All of these values are represented in seconds and will always be integers.

The format of the router.start message is as follows:

{
  "id": "some-router-id",
  "hosts": ["1.2.3.4"],
  "minimumRegisterIntervalInSeconds": 20,
  "prunteThresholdInSeconds": 120
}

After a router.start message is received by a client, the client should send router.register messages. This ensures that the new router can update its routing table and synchronize with existing routers.

If a component comes online after the router, it must make a NATS request called router.greet in order to determine the interval. The response to this message will be the same format as router.start.

The format of the router.register message is as follows:

{
  "host": "127.0.0.1",
  "port": 4567,
  "tls_port": 1234,
  "protocol": "http1",
  "uris": [
    "my_first_url.localhost.routing.cf-app.com",
    "my_second_url.localhost.routing.cf-app.com"
  ],
  "tags": {
    "another_key": "another_value",
    "some_key": "some_value"
  },
  "app": "some_app_guid",
  "stale_threshold_in_seconds": 120,
  "private_instance_id": "some_app_instance_id",
  "isolation_segment": "some_iso_seg_name",
  "server_cert_domain_san": "some_subject_alternative_name"
}

stale_threshold_in_seconds is the custom staleness threshold for the route being registered. If this value is not sent, it will default to the router's default staleness threshold.

app is a unique identifier for an application that the endpoint is registered for. This value will be included in router access logs with the label app_id, as well as being sent with requests to the endpoint in an HTTP header X-CF-ApplicationId.

private_instance_id is a unique identifier for an instance associated with the app identified by the app field. Gorouter includes an HTTP header X-CF-InstanceId set to this value with requests to the registered endpoint.

isolation_segment determines which routers will register route. Only Gorouters configured with the matching isolation segment will register the route. If a value is not provided, the route will be registered only by Gorouters set to the all or shared-and-segments router table sharding modes. Refer to the job properties for [Gorouter] (https://github.com/cloudfoundry/routing-release/blob/develop/jobs/gorouter/spec) for more information.

tls_port is the port that Gorouter will use to attempt TLS connections with the registered backends. Supported only when router.backend.enable_tls: true is configured in the manifest. router.ca_certs may be optionally configured with a CA, for backends certificates signed by custom CAs. For mutual authentication with backends, router.backends.tls_pem may be optionally provided. When router.backend.enable_tls: true, Gorouter will prefer tls_port over port if present in the NATS message. Otherwise, port will be preferred, and messages with only tls_port will be rejected and an error message logged.

server_cert_domain_san (required when tls_port is present) Indicates a string that Gorouter will look for in a Subject Alternative Name (SAN) of the TLS certificate hosted by the backend to validate instance identity. When the value of server_cert_domain_san does not match a SAN in the server certificate, Gorouter will prune the backend and retry another backend for the route if one exists, or return a 503 if it cannot validate the identity of any backend in three tries.

Additionally, if the host and tls_port pair matches an already registered host and port pair, the previously registered route will be overwritten and Gorouter will now attempt TLS connections with the host and tls_port pair. The same is also true if the host and port pair matches an already registered host and tls_port pair, except Gorouter will no longer attempt TLS connections with the backend.

Such a message can be sent to both the router.register subject to register URIs, and to the router.unregister subject to unregister URIs, respectively.

Deleting a Route

Routes can be deleted with the router.unregister nats message. The format of the router.unregister message the same as the router.register message, but most information is ignored. Any route that matches the host, port and uris fields will be deleted.

Example

Create a simple app

$ nohup ruby -rsinatra -e 'get("/") { "Hello!" }' &

Send a register message

$ nats-pub 'router.register' '{"host":"127.0.0.1","port":4567,"uris":["my_first_url.localhost.routing.cf-app.com","my_second_url.localhost.routing.cf-app.com"],"tags":{"another_key":"another_value","some_key":"some_value"}}'

Published [router.register] : '{"host":"127.0.0.1","port":4567,"uris":["my_first_url.localhost.routing.cf-app.com","my_second_url.localhost.routing.cf-app.com"],"tags":{"another_key":"another_value","some_key":"some_value"}}'

See that it works!

$ curl my_first_url.localhost.routing.cf-app.com:8081
Hello!

Unregister the route

$ nats-pub 'router.unregister' '{"host":"127.0.0.1","port":4567,"tls_port":1234,"uris":["my_first_url.localhost.routing.cf-app.com","my_second_url.localhost.routing.cf-app.com"]}'

Published [router.unregister] : '{"host":"127.0.0.1","port":4567,"tls_port":1234,"uris":["my_first_url.localhost.routing.cf-app.com","my_second_url.localhost.routing.cf-app.com"]}'

See that the route is gone

$ curl my_first_url.localhost.routing.cf-app.com:8081
404 Not Found: Requested route ('my_first_url.localhost.routing.cf-app.com') does not exist.

If router.backends.enable_tls has been set to true, tls_port will be used as the definitive port when unregistering a route if present, otherwise port will be used. If router.backends.enable_tls is set to false, port will be preferred and any requests with only tls_port will be rejected and an error logged to the gorouter logs.

Note that if router.backends.enable_tls is true and host and tls_port happens to match a registered host and port pair, this host and port pair will be unregistered. The reverse is also true.

Note

In order to use nats-pub to register a route, you must install the gem on a Cloud Foundry VM. It's easiest on a VM that has ruby as a package, such as the API VM. Find the ruby installed in /var/vcap/packages, export your PATH variable to include the bin directory, and then run gem install nats. Find the nats login info from your gorouter config and use it to connect to the nats cluster.

Health checking from a Load Balancer

To scale Gorouter horizontally for high-availability or throughput capacity, you must deploy it behind a highly-available load balancer (F5, AWS ELB, etc).

Gorouter has a health endpoint /health on port 8443 (with TLS) and on 8080 (without TLS) that returns a 200 OK which indicates the Gorouter instance is healthy; any other response indicates unhealthy. These port can be configured via the router.status.port and router.status.tls.port properties in the BOSH deployment manifest or via the status.port and status.tls.port properties under /var/vcap/jobs/gorouter/config/gorouter.yml

$ curl -v http://10.0.32.15:8080/health
*   Trying 10.0.32.15..
* Connected to 10.0.32.15 (10.0.32.15) port 8080 (#0)
> GET /health HTTP/1.1
> Host: 10.0.32.15:8080
> User-Agent: curl/7.43.0
> Accept: */*
>
< HTTP/1.1 200 OK
< Cache-Control: private, max-age=0
< Expires: 0
< Date: Thu, 22 Sep 2016 00:13:54 GMT
< Content-Length: 3
< Content-Type: text/plain; charset=utf-8
<
ok
* Connection #0 to host 10.0.32.15 left intact

DEPRECATED: Your load balancer can be configured to send an HTTP healthcheck on port 80 with the User-Agent HTTP header set to HTTP-Monitor/1.1. A 200 response indicates the Gorouter instance is healthy; any other response indicates unhealthy. Gorouter can be configured to accept alternate values for the User Agent header using the healthcheck_user_agent configuration property; as an example, AWS ELBS send User-Agent: ELB-HealthChecker/1.0.

$ curl -v -A "HTTP-Monitor/1.1" "http://10.0.32.15"
* Rebuilt URL to: http://10.0.32.15/
* Hostname was NOT found in DNS cache
*   Trying 10.0.32.15...
* Connected to 10.0.32.15 (10.0.32.15) port 80 (#0)
> GET / HTTP/1.1
> User-Agent: HTTP-Monitor/1.1
> Host: 10.0.32.15
> Accept: */*
>
< HTTP/1.1 200 OK
< Cache-Control: private, max-age=0
< Expires: 0
< X-Vcap-Request-Id: 04ad84c6-43dd-4d20-7818-7c47595d9442
< Date: Thu, 07 Jan 2016 22:30:02 GMT
< Content-Length: 3
< Content-Type: text/plain; charset=utf-8
<
ok
* Connection #0 to host 10.0.32.15 left intact

DEPRECATED: The /healthz endpoint is now an alias for the /health endpoint to ensure backward compatibility.

Load Balancing

The Gorouter is, in simple terms, a reverse proxy that load balances between many backend instances. The default load balancing algorithm that Gorouter will use is a simple round-robin strategy. Gorouter will retry a request if the chosen backend does not accept the TCP connection.

Round-Robin

Default load balancing algorithm that gorouter will use or may be explicitly set in gorouter.yml yaml default_balancing_algorithm: round-robin

Least-Connection

The Gorouter also supports least connection based routing and this can be enabled in gorouter.yml

default_balancing_algorithm: least-connection

Least connection based load balancing will select the endpoint with the least number of connections. If multiple endpoints match with the same number of least connections, it will select a random one within those least connections.

Note

Gorouter currently only supports changing the load balancing strategy at the gorouter level and does not yet support a finer-grained level such as route-level. Therefore changing the load balancing algorithm from the default (round-robin) should be proceeded with caution.

Implementation of customizable LB Algorithm (per-route) is being tracked in RFC-0027

When terminating TLS in front of Gorouter with a component that does not support sending HTTP headers

Enabling apps and CF to detect that request was encrypted using X-Forwarded-Proto

If you terminate TLS in front of Gorouter, your component should send the X-Forwarded-Proto HTTP header in order for applications and Cloud Foundry system components to correctly detect when the original request was encrypted. As an example, UAA will reject requests that do not include X-Forwarded-Proto: https.

If your TLS-terminating component does not support sending HTTP headers, we recommend also terminating TLS at Gorouter. In this scenario you should only disable TLS at Gorouter if your TLS-terminating component rejects unencrypted requests and your private network is completely trusted. In this case, use the following property to inform applications and CF system components that requests are secure.

properties:
  router:
    force_forwarded_proto_https: true

Enabling apps to detect the requestor's IP address using PROXY Protocol

If you terminate TLS in front of Gorouter, your component should also send the X-Forwarded-Proto HTTP header in order for X-Forwarded-For header to applications can detect the requestor's IP address.

If your TLS-terminating component does not support sending HTTP headers, you can use the PROXY protocol to send Gorouter the requestor's IP address.

If your TLS-terminating component supports the PROXY protocol, enable the PROXY protocol on Gorouter using the following cf-deployment manifest property:

properties:
  router:
    enable_proxy: true

You can test this feature manually:

echo -e "PROXY TCP4 1.2.3.4 [GOROUTER IP] 12345 [GOROUTER PORT]\r\nGET / HTTP/1.1\r\nHost: [APP URL]\r\n" | nc [GOROUTER IP] [GOROUTER PORT]

You should see in the access logs on the Gorouter that the X-Forwarded-For header is 1.2.3.4. You can read more about the PROXY Protocol here.

HTTP/2 Support

The Gorouter supports ingress and egress HTTP/2 connections when the BOSH deployment manifest property is enabled.

properties:
  router:
    enable_http2: true

By default, connections will be proxied to backends over HTTP/1.1, regardless of ingress protocol. Backends can be configured with the http2 protocol to enable end-to-end HTTP/2 routing for use cases like gRPC.

Example router.register message with http2 protocol:

{
  "host": "127.0.0.1",
  "port": 4567,
  "protocol": "http2",
  "...": "..."
}

Headers

If a user wants to send requests to a specific app instance, the header X-CF-APP-INSTANCE can be added to indicate the specific instance to be targeted. The format of the header value should be X-Cf-App-Instance: APP_GUID:APP_INDEX. If the instance cannot be found or the format is wrong, a 400 status code is returned. In addition, Gorouter will return a X-Cf-Routererror header. If the instance guid provided is incorrectly formatted, the value of the header will be invalid_cf_app_instance_header. If the instance guid provided is correctly formatted, but the guid does not exist, the value of this header will be unknown_route, and the request body will contain 400 Bad Request: Requested instance ('1') with guid ('aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa') does not exist for route ('dora.superman.routing.cf-app.com').

Usage of the X-Cf-App-Instance header is only available for users on the Diego architecture.

Router Errors

The value of the X-Cf-Routererror header can be one of the following:

Value Description
invalid_cf_app_instance_header The provided value for the "X-Cf-App-Instance" header does not match the required format of APP_GUID:INSTANCE_ID.
empty_host The value for the "Host" header is empty, or the "Host" header is equivalent to the remote address. Some LB's optimistically set the "Host" header value with their IP address when there is no value present.
unknown_route The desired route does not exist in the gorouter's route table.
no_endpoints There is an entry in the route table for the desired route, but there are no healthy endpoints available.
Connection Limit Reached The backends associated with the route have reached their max number of connections. The max connection number is set via the spec property router.backends.max_conns.
route_service_unsupported Route services are not enabled. This can be configured via the spec property router.route_services_secret. If the property is empty, route services are disabled.
endpoint_failure The registered endpoint for the desired route failed to handle the request.