ui: websocket watchers and http2

[chrisroberts]

Description

The HTTP API currently only supports HTTP/1 and this leads to issues within the UI, especially on chromium based browsers, where the maximum number of HTTP/1 connections is limited. The UI makes use of watchers, which are blocking requests that wait for a change to occur and update the UI. In some places the number of watchers combined with other requests will exceed the limit and result in the UI becoming unresponsive until a transition is made or the page is reloaded.

To remove the connection limit restriction, the UI watchers have been updated to use WebSockets for the blocking requests. The use of WebSockets for watchers happens at request time, so there is no need for refactoring or updating the existing UI implementations. This also allows the use of WebSockets for watchers to be enabled or disabled with a configuration flag (or dynamically based on condition).

Unfortunately, websockets are not available for FIPS builds due to WebSocket's reliance on SHA1 for the handshake and SHA1 not being available within go when FIPS is enabled. To rectify the original issue of the UI becoming unresponsive when WebSockets are not available, enabling HTTP/2 fixes the issue. Note that the UI still uses WebSockets for terminal emulation, and that will be unavailable on FIPS builds.

Ultimately this changeset fixes the issue of the UI becoming unresponsive in two ways and which fix is used is dependent on the Nomad configuration.

WebSockets are used if:

• TLS is disabled (which is required for browsers to use HTTP/2)
• HTTP/2 is disabled in the config

HTTP/2 is used if:

• it is available 🙂

Testing & Reproduction steps

Links

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Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

[tgross]

LGTM! Nice work on figuring out this mess of complexity