Trade-offs in AWS ElastiCache

import getpass
import time
import redis

client = redis.Redis(
    host="cache-test.example.com", port=6379,
    username=input("Test cache username (blank if unused): ") or None,
    password=getpass.getpass("Test cache password: "),
    ssl=True, ssl_cert_reqs="required",
    socket_connect_timeout=5, socket_timeout=5,
    decode_responses=True,
)
client.ping()
prefix = "tradeoff-cache-check:"
if next(client.scan_iter(match=prefix + "*"), None) is not None:
    raise RuntimeError("Test keys already exist; inspect them before retrying")
source = {"product-a": "price=25", "product-b": "price=70"}
first_evictions = int(client.info("stats")["evicted_keys"])
inserted = 0
misses = 0
observed_eviction = False
started = time.monotonic()
try:
    for key, value in source.items():
        client.set(prefix + key, value, ex=300)
    for i in range(32768):
        client.set(prefix + "filler:" + str(i), "x" * 65536, ex=300)
        inserted = i + 1
        for key, authoritative in source.items():
            value = client.get(prefix + key)
            if value is None:
                misses += 1
                value = authoritative
                client.set(prefix + key, value, ex=300)
            if value != authoritative:
                raise RuntimeError("Incorrect application value for " + key)
        if i % 64 == 0:
            observed_eviction = (
                int(client.info("stats")["evicted_keys"]) > first_evictions
            )
            if observed_eviction:
                break
    print({"keys_written": inserted, "fixture_misses": misses,
           "elapsed_seconds": round(time.monotonic() - started, 2),
           "eviction_observed": observed_eviction})
    if not observed_eviction:
        raise RuntimeError("INCONCLUSIVE: payload cap reached without eviction")
finally:
    # Only this run's known keys; no FLUSHDB or wildcard deletion.
    for i in range(inserted):
        client.delete(prefix + "filler:" + str(i))
    for key in source:
        client.delete(prefix + key)
    client.close()