HTML Applications

Another way to implement the UI is with HTML-based user interfaces. Every microservice has one or more web pages that are generated on the server. These web pages can also use JavaScript. Here, unlike SPAs, only a new HTML web page and not necessarily an application, is loaded by the server when changing between web pages.

ROCA

ROCA (resource-oriented client architecture)[1] proposes a way to arrange the handling of JavaScript and dynamic elements in HTML user interfaces. ROCA views itself as

HTML User Interface with an Asset Server

Figure 8.4 HTML User Interface with an Asset Server

an alternative to SPAs. In ROCA the role of JavaScript is limited to optimizing the usability of the web pages. JavaScript can facilitate their use or can add effects to the HTML web pages. However, the application has to remain usable without JavaScript. It is not the purpose of ROCA that users really use web pages without JavaScript. The applications are only supposed to use the architecture of the web, which is based on HTML and HTTP. Also ROCA makes sure that all logic is actually implemented on the server instead of JavaScript on the client. That way other clients can use the very same logic.

When a web application is divided into microservices, ROCA reduces the dependencies and simplifies the division. Between microservices the coupling of the UI can be achieved by links. For HTML applications links are the usual tool for navigating between web pages and represent a natural integration. There are no foreign bodies as in the case of SPAs.

To help with the uniformity of the HTML user interfaces, the microservices can use a shared asset server the same was as SPAs can (see Figure 8.4). It contains all the CSS and JavaScript libraries. If the teams create design guidelines for the HTML web pages and look after the assets on the asset server, the user interfaces of the different microservices will be largely identical. However, as discussed previously, this will lead to code dependencies between the UIs of the microservices.

  • [1] http://roca-style.org/
 
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