Reactive Infrastructure

This section covers basic information on the reactive programming support using Spring Vault.

What is Reactive Programming?

In plain terms reactive programming is about non-blocking applications that are asynchronous and event-driven and require a small number of threads to scale vertically (i.e. within the JVM) rather than horizontally (i.e. through clustering).

A key aspect of reactive applications is the concept of backpressure which is a mechanism to ensure producers don’t overwhelm consumers. For example in a pipeline of reactive components extending from the database to the HTTP response when the HTTP connection is too slow the data repository can also slow down or stop completely until network capacity frees up.

Reactive Vault Client

Spring Vault’s reactive client support is built on top of composable authentication steps and Spring’s functional WebClient via Reactor Netty or Jetty, which feature both a fully non-blocking, event-driven HTTP client.

It exposes VaultTokenSupplier as supplier of VaultToken to authenticate HTTP requests and ReactiveVaultOperations as the primary entry point. The core configuration of VaultEndpoint, ClientOptions and SSL are reused across the various client implementation.

The class ReactiveVaultTemplate, located in the package org.springframework.vault.core, is the central class of the Spring’s reactive Vault support providing a rich feature set to interact with Vault. The template offers convenience operations to read, write and delete data in Vault and provides a mapping between your domain objects and Vault data.

Once configured, ReactiveVaultTemplate is thread-safe and can be reused across multiple instances.

The mapping between Vault documents and domain classes is done by delegating to WebClient and its codecs.

The ReactiveVaultTemplate class implements the interface ReactiveVaultOperations. In as much as possible, the methods on ReactiveVaultOperations are named after methods available on the Vault API to make the API familiar to existing Vault developers who are used to the API and CLI. For example, you will find methods such as "write", "delete", and "read". The design goal was to make it as easy as possible to transition between the use of the Vault API and ReactiveVaultOperations. A major difference in between the two APIs is that ReactiveVaultOperations can be passed domain objects instead of JSON Key-Value pairs.

The preferred way to reference the operations on ReactiveVaultTemplate instance is via its interface ReactiveVaultOperations.

Functionality not explicitly exposed by the ReactiveVaultTemplate you can use one of several execute callback methods to access underlying APIs. The execute callbacks will give you a reference to a WebClient object. Please see the section Execution Callbacks for more information.

Now let’s look at examples of how to work with Vault in the context of the Spring container.

Registering and configuring Spring Vault beans

Using Spring Vault does not require a Spring Context. However, instances of ReactiveVaultTemplate and VaultTokenSupplier registered inside a managed context will participate in lifecycle events provided by the Spring IoC container. This is useful to dispose active Vault sessions upon application shutdown. You also benefit from reusing the same ReactiveVaultTemplate instance across your application.

Spring Vault comes with a supporting configuration class that provides bean definitions for use inside a Spring context. Application configuration classes typically extend from AbstractVaultConfiguration and are required to provide additional details that are environment specific.

Extending from AbstractVaultConfiguration requires to implement ` VaultEndpoint vaultEndpoint()` and ClientAuthentication clientAuthentication() methods.

Example 1. Registering Spring Vault objects using Java based bean metadata

@Configuration
public class AppConfig extends AbstractReactiveVaultConfiguration {

    /**
     * Specify an endpoint for connecting to Vault.
     */
    @Override
    public VaultEndpoint vaultEndpoint() {
        return new VaultEndpoint();                            (1)
    }

    /**
     * Configure a client authentication.
     * Please consider a more secure authentication method
     * for production use.
     */
    @Override
    public ClientAuthentication clientAuthentication() {
        return new TokenAuthentication("…");                   (2)
    }
}

1	Create a new `VaultEndpoint` that points by default to `https://localhost:8200`.
2	This sample uses `TokenAuthentication` to get started quickly. See [vault.core.authentication] for details on supported authentication methods.

Session Management

Spring Vault requires a token to authenticate Vault requests. See [vault.core.authentication] on details regarding authentication. The reactive client requires a non-blocking token supplier whose contract is defined in VaultTokenSupplier. Tokens can be static or obtained through a declared authentication flow. Vault login should not occur on each authenticated Vault interaction but the session token should be kept across a session. This aspect is handled by a session manager implementing ReactiveSessionManager, such as ReactiveLifecycleAwareSessionManager.

Execution callbacks

One common design feature of all Spring template classes is that all functionality is routed into one of the templates execute callback methods. This helps ensure that exceptions and any resource management that maybe required are performed consistency. While this was of much greater need in the case of JDBC and JMS than with Vault, it still offers a single spot for access and logging to occur. As such, using the execute callback is the preferred way to access the Vault API to perform uncommon operations that we’ve not exposed as methods on ReactiveVaultTemplate.

Here is a list of execute callback methods.

<T> T doWithVault (Function<WebClient, ? extends T> clientCallback) Composes a reactive sequence the given WebClient, allows to interact with Vault without a session context.
<T> T doWithSession (Function<WebClient, ? extends T> clientCallback) Composes a reactive sequence the given WebClient, allows to interact with Vault in an authenticated session.

Here is an example that uses the callback to initialize Vault:

reactiveVaultOperations.doWithVault(webClient -> {

    return webClient.put()
                    .uri("/sys/init")
                    .syncBody(request)
                    .retrieve()
                    .toEntity(VaultInitializationResponse.class);
});