Local-first software has the potential to offer users a great experience by combining the best aspects of traditional applications with cloud-based applications. However, not much has been documented regarding developing backends for local-first software, particularly one that is scalable while still supporting end-to-end encryption. This thesis presents a backend architecture that was then implemented and evaluated. The implementation was shown to be scalable and was able to maintain an estimated end-to-end latency of around 30-50ms as the number of simulated clients increased. The architecture supports end-to-end encryption to offer user privacy and to ensure that neither cloud nor service providers can access user data. Furthermore, by occasionally performing snapshots the encryption overhead was shown to be manageable compared to the raw data, at around 18.2% in the best case and 118.9% when using data from automerge-perf, a standard benchmark. Lastly, the processing times were shown to be upwards of 50 times faster when using snapshots compared to handling individual changes.

Mobile applications often must synchronize their local state with a backend to maintain an up-to-date view of the application state. Nevertheless, in some cases, the application’s ability to work offline or with poor network connectivity may be more significant than guaranteeing strong consistency. We present a method to structure the application state in a portable way using the Redux pattern and the properties of strongly typed languages. This method allows employing Conflict-free Replicated Data Types to create a custom converging state: this way, each replica can edit its local state autonomously and merge conflicts with other replicas when possible. Furthermore, we propose to keep a server as the communication channel and analyze how this architecture impacts design choices and optimizations related to CRDTs. Finally, we evaluate our method on a note-taking application using a few well-known CRDT designs and quantitatively justify our design choices. / Mobilapplikationer måste ofta synkronisera lokala tillstånd med backend för att upprätthålla en uppdaterad vy av applikationstillstånd. I vissa fall kan dock applikationens förmåga att arbeta offline eller med dålig nätverksanslutning vara viktigare än att garantera strong consistency. Vi presenterar en metod för att strukturera applikationstillståndet på ett portabelt sätt med hjälp av Redux-mönstret och egenskaperna hos starkt typade språk. Den här metoden gör det möjligt att använda Conflict-free Replicated Data Types för att skapa ett anpassat konvergerande tillstånd: på så sätt kan varje replik redigera sin lokala status självständigt och slå samman konflikter med andra repliker när det är möjligt. Dessutom föreslår vi att behålla en server som kommunikationskanal och analysera hur denna arkitektur påverkar designval och optimeringar relaterade till CRDT. Slutligen utvärderar vi vår metod på en anteckningsapplikation med några välkända CRDT-designer och motiverar kvantitativt våra designval. / Le applicazioni mobile spesso devono sincronizzare il loro stato locale con il back-end per mantenere una visione aggiornata dello stato dell’applicazione. Tuttavia, in alcuni casi, la capacità dell’applicazione di funzionare offline o con una scarsa connettività può essere più importante del garantire la “strong consistency”. In questa tesi presentiamo un metodo per strutturare lo stato di un’applicazione in modo portabile utilizzando il pattern Redux e le proprietà dei linguaggi fortemente tipizzati. Questo metodo consente di utilizzare i Conflict-free Replicated Data Types per creare uno stato convergente ad hoc: in questo modo, ogni replica può modificare il proprio stato locale in modo autonomo e risolvere i conflitti con le altre repliche quando possibile. Inoltre, proponiamo di mantenere un server come canale di comunicazione e di analizzare come questa architettura influisca sulle scelte progettuali e sulle ottimizzazioni relative ai CRDT. Infine, valutiamo il nostro metodo su un’applicazione per prendere appunti utilizzando alcuni CRDT noti e giustifichiamo quantitativamente le nostre scelte di progettazione.