This topic describes how the Gorouter, the main component in the PWS routing tier, routes HTTP traffic within Pivotal Web Services.
For more information, see the Routing section of the PWS Components topic.
The Gorouter has a limit of 1 MB for HTTP Headers.
X-Forwarded-Proto header gives the scheme of the HTTP request from the client.
If an incoming request includes the
X-Forwarded-Proto header, the Gorouter:
- Appends it to the existing header
- Sets the scheme to HTTP if the client made an insecure request, meaning a request on port 80
- Sets the scheme to HTTPS if the client made a secure request, meaning a request on port 443
Developers can configure their apps to reject insecure requests by inspecting the
X-Forwarded-Proto HTTP header on incoming traffic. The header may have multiple values represented as a comma-separated list, so developers must ensure the app rejects traffic that includes any
X-Forwarded-Proto values that are not HTTPS.
X-Forwarded-For is present, the Gorouter appends the load balancer’s IP address to it and forwards the list. If
X-Forwarded-For is not present, then the Gorouter sets it to the IP address of the load balancer in the forwarded request (some load balancers masquerade the client IP). If a load balancer sends the client IP using the PROXY protocol, then the Gorouter uses the client IP address to set
If your load balancer terminates TLS on the client side of the Gorouter, it must append these headers to requests forwarded to the Gorouter.
Zipkin is a tracing system that enables app developers to troubleshoot failures or latency issues. Zipkin provides the ability to trace requests and responses across distributed systems. For more information, see Zipkin.io.
The Gorouter examines the HTTP request headers and performs the following:
- If the
X-B3-SpanIdHTTP headers are not present in the request, the Gorouter generates values for these and inserts the headers into the request forwarded to an app. These values are also found in the Gorouter access log message for the request:
- If the
X-B3-SpanIdHTTP headers are present in the request, the Gorouter forwards them unmodified. In addition to these trace and span IDs, the Gorouter access log message for the request includes
Developers can then add Zipkin trace IDs to their app logging in order to trace app requests and responses in PWS.
After adding Zipkin HTTP headers to app logs, developers can use
cf logs myapp to correlate the trace and span IDs logged by the Gorouter with the trace ids logged by their app. To correlate trace IDs for a request through multiple apps, each app must forward appropriate values for the headers with requests to other applications.
Developers who want to obtain debug data for a specific instance of an app can use the HTTP header
X-CF-APP-INSTANCE to make a request to an app instance.
To make an HTTP request to a specific app instance:
Obtain the GUID of your app:
$ cf app YOUR-APP --guid
List your app instances and retrieve the index number of the instance you want to debug:
$ cf app YOUR-APP
Make a request to the app route using the HTTP header
X-CF-APP-INSTANCEset to the concatenated values of the app GUID and the instance index:
$ curl app.example.com -H "X-CF-APP-INSTANCE":"YOUR-APP-GUID:YOUR-INSTANCE-INDEX"
Apps that require mutual TLS (mTLS) need metadata from client certificates to authorize requests. PWS supports this use case without bypassing layer-7 load balancers and the Gorouter.
The HTTP header
X-Forwarded-Client-Cert (XFCC) may be used to pass the originating client certificate along the data path to the application. Each component in the data path must trust that the back end component has not allowed the header to be tampered with.
If you configure the load balancer to terminate TLS and set the XFCC header from the received client certificate, you must also configure the load balancer to strip this header if it is present in client requests. This configuration is required to prevent spoofing of the client certificate.
The following sections describe supported deployment configurations.
By default, the Gorouter forwards arbitrary headers that are not otherwise mentioned in the docs. This includes the XFCC header.
For apps to receive the XFCC header, configure your load balancer to set the XFCC header with the contents of the client certificate received in the TLS handshake.
To enable this mode, select the Infrastructure load balancer option for TLS termination point in the Networking pane of the PAS tile.
This option allows you to configure support for the XFCC header while leveraging HAProxy. When selected, HAProxy sets the XFCC header to the contents of the client certificate received in the TLS handshake.
This option requires you to configure the load balancer in front of HAProxy to pass through the TLS handshake to HAProxy through TCP.
To enable this mode, select the HAProxy option for TLS termination point in the Networking configuration screen of the PAS tile.
HAProxy trusts the Diego intermediate certificate authority. This trust is enabled automatically and permits mutual authentication between apps running on PWS.
If the Gorouter is the first component to terminate TLS, such that it receives the certificate of the originating client in the mutual TLS handshake, you should select this option. When selected, the Gorouter sets the XFCC header to the contents of the client certificate received in the TLS handshake and strips the XFCC header when present in a request.
This option requires you to configure the load balancer in front of the Gorouter to pass through TLS handshake to the Gorouter through TCP.
To enable this mode, select the Router option for TLS termination point in the Networking pane of the PAS tile.
The Gorouter trusts the Diego intermediate certificate authority. This trust is enabled automatically and permits mutual authentication between apps running on PWS.
Depending on your needs, you can configure your deployment to terminate TLS at the Gorouter, at the Gorouter and the load balancer, or at the load balancer only.
The Gorouter supports TLS and mutual authentication to back end destinations, including app instances, platform services, and any other routable endpoints.
To enable this feature, see Configure Validation of App Instance Identity with TLS.
As PWS manages and balances apps, the internal IP address and ports for app instances change. To keep the Gorouter’s routing tables current, a Route-Emitter on each Diego cell sends a periodic update to all Gorouters through NATS to remind them of the location of all app instances. The default frequency of these updates is 20 seconds. The Gorouter tracks a time-to-live (TTL) for each route to back end mapping. This TTL defaults to 120 seconds and is reset when the Gorouter receives an updated registration message.
Network partitions or NATS failures can cause the Gorouter’s routing table to fall out of sync, as PWS continues to re-create containers across hosts to keep apps running. This can lead to routing of requests to incorrect destinations.
You can configure the Gorouter to handle this problem in two ways:
|Consistency mode||Security of traffic between Gorouter and Containers||Gorouter Route Pruning|
|With TLS Enabled||Encrypted via TLS||Routes are pruned on failure of TLS handshake only.|
|Without TLS Enabled||Plain text||Routes are pruned on TTL expiry|
Both of these consistency modes are described below.
This consistency mode is newer and has the following benefits:
- Improved availability for apps by keeping routes in the Gorouter’s routing table when TTL expires
- Increased guarantees against misrouting by validating the identity of back ends before forwarding requests
- Increased security by encrypting data in flight from the Gorouter to back ends
Warning: TLS routing requires an additional 32 MB of RAM capacity on your Diego Cells per app instance, as well as additional CPU capacity. Check the total amount of Diego Cell memory available to allocate in your environment, and if it is less than 32 MB times the number of running app instances, scale out your Diego Cells.
Warning: You may see an increase of memory and CPU usage for your Gorouters after enabling TLS routing. Check the total amount of memory and CPU usage of the Gorouters in your environment, and if they are close to the size limit, consider scaling out your Gorouters before enabling TLS routing.
In this mode, the Diego Route-Emitters send a modified route registration message to NATS that includes a unique identifier for the app instance, as well instructions to use TLS when communicating with the instance. For more information, see TLS to Apps and Other Back End Services.
Before forwarding traffic to an app instance, the Gorouter initiates a TLS handshake with an Envoy proxy running in each app container. In the TLS handshake, the Envoy proxy presents a certificate generated by Diego for each container which uniquely identifies the container using the same app instance identifier sent by the Route-Emitter, configured in the certificate as a domain Subject Alternative Name (SAN). For more information, see Envoyproxy.io.
If the Gorouter confirms that the app instance identifier in the certificate matches the one received in the route registration message, the Gorouter forwards the HTTP request over the TLS session, and the Envoy proxy then forwards it to the app process. If the instance identifiers do not match, the Gorouter removes the app instance from its routing table and transparently retries another instance of the app.
Verifying app identity using TLS improves resiliency and consistency for app routes. The App Containers pane of the PAS tile includes the following options:
Breaking Change: If you have mutual TLS app identity verification enabled, app containers accept incoming communication only from the Gorouter. This disables TCP routing.
Note: This feature does not work if the Disable SSL certificate verification for this environment checkbox is enabled in the Networking pane of the PAS tile.
- Router uses TLS to verify app identity
- Enables the Gorouter to verify app identity using TLS. This is the default option.
- Router and apps use mutual TLS to verify each other’s identity
- Enables the Gorouter and your apps to verify each other’s identity using TLS.
In this consistency mode, the Diego Route-Emitters on each cell send route registration messages that include instructions for the Gorouter to send unencrypted requests to the app instance. If the Gorouter does not receive an update for the route within the time-to-live (TTL) interval, the route is pruned from the Gorouter’s routing table. For more information, see TLS to Apps and Other Back End Services.
This pruning method was developed before the alternative was available.
The Gorouter can be configured to use different load balancing algorithms for routing incoming requests to app instances. The Gorouter maintains a dynamically updated list of app instances for each route. Depending on which algorithm is selected, it forwards to one of the app instances.
To configure the behavior, you can change the value of
router.balancing_algorithm manifest property. The available options are:
By default, the Gorouter uses the round-robin algorithm.
Incoming requests for a given route are forwarded to all app instances one after another, looping back to the first one after they have each received a request. This algorithm is suitable for most use cases and evenly distributes the load between app instances.
Each request for a given route is forwarded to the app instance with the least number of open connections. This algorithm can be more suitable for some cases. For example, if app instances have long-lived connections and are scaled up, then new instances receive fewer connections, causing a disproportionate load. In this case, choosing a least-connection algorithm sends new connections to new instances to equalize the load.
WebSockets is a protocol providing bi-directional communication over a single, long-lived TCP connection, commonly implemented by web clients and servers. WebSockets are initiated through HTTP as an upgrade request. The Gorouter supports this upgrade handshake, and holds the TCP connection open with the selected app instance.
The Gorouter supports session affinity, or sticky sessions, for incoming HTTP requests to compatible apps.
With sticky sessions, when multiple instances of an app are running on Cloud Foundry, requests from a particular client always reach the same app instance. This allows apps to store session data specific to a user session.
To support sticky sessions, configure your app to return a sticky session cookie in responses. Gorouter supports
If an app returns a sticky session cookie to a client request, the CF routing tier generates a unique
VCAP_IDfor the app instance based on its GUID in the following format:
On subsequent requests, the client must provide both the sticky session and
The CF routing tier uses the
VCAP_ID cookie to forward client requests to the same app instance every time. The sticky session cookie is forwarded to the app instance to enable session continuity. If the app instance identified by the
VCAP_ID crashes, the Gorouter attempts to route the request to a different instance of the app. If the Gorouter finds a healthy instance of the app, it initiates a new sticky session.
Note: Cloud Foundry does not persist or replicate HTTP session data across app instances. If an app instance crashes or is stopped, session data for that instance is lost. If you require session data to persist across crashed or stopped instances, or to be shared by all instances of an app, store session data in a CF marketplace service that offers data persistence.
The Gorouter supports keep-alive connections from clients and does not close the TCP connection with clients immediately after returning an HTTP response. Clients are responsible for closing these connections.
If keep-alive connections are disabled, the Gorouter closes the TCP connection with an app instance or system component after receiving an HTTP response.
If keep-alive connections are enabled, the Gorouter maintains established TCP connections to back ends. The Gorouter supports up to 10 idle connections to each back end:
- If an idle connection exists for a given back end, the Gorouter reuses it to route subsequent requests.
- If no idle connection exists for this back end, the Gorouter creates a new connection.
If the Gorouter cannot establish a TCP connection with a selected app instance, the Gorouter considers the instance ineligible for requests for 30 seconds and transparently attempts to connect to another app instance. Once the Gorouter has established a TCP connection with an app instance, the Gorouter forwards the HTTP request.
When you deploy an app that requires Diego Cells to restart or recreate, the app may not respond to a Gorouter request before the keep-alive connection breaks. The following table describes how the Gorouter behaves if it cannot establish a TCP connection to an app:
|If the Gorouter…||and the back end…||then the Gorouter…|
|cannot establish a TCP connection to a back end||N/A||retries another back end, no more than 3 times|
|establishes a TCP connection to a back end and forwards the request||does not respond||waits 15 minutes for a response, and if it errors, does not retry another back end|
|establishes a TCP connection to a back end and forwards the request||returns a TCP connection error||returns an error to the client, marks backend ineligible, and does not retry another back end|
In all cases, if the app still does not respond to the request, the Gorouter returns a
502 error. For more information, see Troubleshooting Router Error Responses.