LLM Application Architecture

Overview

LLM application architecture focuses on building reliable AI features around a model. The model is only one component. Retrieval, caching, safety checks, and observability are equally important.

Reference Architecture

flowchart LR
    A[Client] --> B[API Gateway]
    B --> C[Application Service]
    C --> D[Prompt Builder]
    C --> E[Retrieval Service]
    D --> F[LLM Provider]
    E --> G[Vector Store]
    C --> H[Policy and Guardrails]
    C --> I[Telemetry]

Practical Example - Service Composition in C#

public interface IAnswerService
{
    Task<string> AnswerAsync(string question, CancellationToken ct);
}

public sealed class AnswerService : IAnswerService
{
    private readonly IRetrievalService _retrieval;
    private readonly ILlmClient _llm;

    public AnswerService(IRetrievalService retrieval, ILlmClient llm)
    {
        _retrieval = retrieval;
        _llm = llm;
    }

    public async Task<string> AnswerAsync(string question, CancellationToken ct)
    {
        var context = await _retrieval.GetContextAsync(question, ct);
        var prompt = $"Use only the context below.\\n{context}\\nQuestion: {question}";
        return await _llm.CompleteAsync(prompt, ct);
    }
}

Production Example - Failure Handling

Production systems should include:

Common Pitfalls

Key Takeaways