Di Session

1"""AWS client construction for the dynamic-instrumentation host scripts.
2
3WHY THIS EXISTS
4``di_app_signals_client.py`` (application-signals client) and ``di_logs_client.py``
5(CloudWatch Logs client) both build a boto3 client the same way: an
6``AWS_PROFILE``-scoped session and a client whose region comes from
7``di_region.resolve_region``. Centralizing that construction here keeps the two
8client seams from drifting apart, mirroring how ``di_region`` already centralizes
9the region precedence the client depends on.
10
11POLICY
12* ``AWS_PROFILE`` selects credentials only (the profile's configured region is
13  ignored — region comes from ``resolve_region``).
14* The region is resolved at call time via ``di_region.resolve_region`` so a
15  ``--region`` flag (set into ``AWS_REGION`` by the entry script) or the env vars
16  take effect.
17* ``boto3`` is imported lazily inside the function so importing this module never
18  requires boto3. (``--print-contract`` is a separate matter: it resolves the op
19  functions, which transitively import ``botocore`` via the op modules — only a bare
20  ``import di_instrumentation``/``di_snapshots`` is boto3-free.)
21
22Per-surface concerns stay with the caller, not here:
23* the application-signals SDK-version guard and its client cache live in
24  ``di_app_signals_client.get_application_signals_client``;
25* the lazy ``logs_client`` proxy cache lives in ``di_logs_client``.
26"""
27
28import os
29
30from di_region import resolve_region
31
32
33def build_client(service_name: str):
34    """Build a boto3 client for ``service_name`` using the shared profile + region policy.
35
36    Args:
37        service_name: The boto3 service name, e.g. ``"application-signals"`` or ``"logs"``.
38
39    Returns:
40        A boto3 client whose credentials come from ``AWS_PROFILE`` (or the ambient
41        default chain) and whose region comes from ``di_region.resolve_region``.
42    """
43    import boto3
44
45    session = boto3.Session(profile_name=os.environ.get("AWS_PROFILE"))
46    return session.client(service_name, region_name=resolve_region())