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Core CDN Cache simulation.
Implements full OpenEnv interface: reset(), step(), state()
"""
from collections import defaultdict
from typing import Dict, Optional, List, Tuple
from env.models import (
Observation, Action, Reward, StepResult, FileEntry, TaskConfig
)
from env.traffic import TrafficGenerator
TASK_CONFIGS = {
"task_easy": TaskConfig(
task_id="task_easy",
name="Steady Traffic Cache",
difficulty="easy",
cache_capacity_mb=100.0,
num_files=30,
viral_ratio=0.0, # no viral files
episode_length=100,
description=(
"Cache has 100MB capacity. Only steady traffic files. "
"Agent must learn LRU-style eviction. Target hit rate >= 0.60."
),
),
"task_medium": TaskConfig(
task_id="task_medium",
name="Mixed Traffic Cache",
difficulty="medium",
cache_capacity_mb=80.0,
num_files=50,
viral_ratio=0.2,
episode_length=150,
description=(
"80MB cache, mix of steady and viral files. "
"Agent must prioritize popular content and handle viral spikes. "
"Target hit rate >= 0.55 with efficient eviction."
),
),
"task_hard": TaskConfig(
task_id="task_hard",
name="Constrained Cache with Viral Bursts",
difficulty="hard",
cache_capacity_mb=50.0,
num_files=80,
viral_ratio=0.35,
episode_length=200,
description=(
"Tight 50MB cache, many viral bursts, large file sizes. "
"Agent must predict spikes, avoid cache thrashing, "
"and maximize bandwidth saved. Target hit rate >= 0.45."
),
),
}
class CDNCacheEnv:
"""
CDN Cache Optimizer Environment.
At each step, a file is requested. If not cached, agent must decide
which file (if any) to evict to make room for the new one.
"""
def __init__(self, task_id: str = "task_easy", seed: int = 42):
if task_id not in TASK_CONFIGS:
raise ValueError(f"Unknown task_id: {task_id}. Choose from {list(TASK_CONFIGS.keys())}")
self.config = TASK_CONFIGS[task_id]
self.seed = seed
self._cache: Dict[str, FileEntry] = {} # file_id -> FileEntry
self._cache_used_mb: float = 0.0
self._step: int = 0
self._hits: int = 0
self._misses: int = 0
self._recent_hits: List[bool] = []
self._last_evicted: Optional[str] = None
self._eviction_counts: Dict[str, int] = defaultdict(int)
self._total_bandwidth_saved: float = 0.0
self._done: bool = False
self.traffic = TrafficGenerator(
num_files=self.config.num_files,
viral_ratio=self.config.viral_ratio,
episode_length=self.config.episode_length,
seed=seed,
)
# ─────────────────────────────────────────────
# OpenEnv Interface
# ─────────────────────────────────────────────
def reset(self) -> Observation:
"""Reset environment to initial state."""
self._cache = {}
self._cache_used_mb = 0.0
self._step = 0
self._hits = 0
self._misses = 0
self._recent_hits = []
self._last_evicted = None
self._eviction_counts = defaultdict(int)
self._total_bandwidth_saved = 0.0
self._done = False
self.traffic = TrafficGenerator(
num_files=self.config.num_files,
viral_ratio=self.config.viral_ratio,
episode_length=self.config.episode_length,
seed=self.seed,
)
return self._make_observation(cache_hit=False)
def step(self, action: Action) -> StepResult:
"""Process one step: handle eviction, then serve the request."""
if self._done:
raise RuntimeError("Episode done. Call reset() first.")
file_id, size_mb, is_viral = self.traffic.get_request(self._step)
cache_hit = file_id in self._cache
reward = self._process_step(action, file_id, size_mb, is_viral, cache_hit)
self._step += 1
self._done = self._step >= self.config.episode_length
obs = self._make_observation(cache_hit=cache_hit)
info = {
"total_hits": self._hits,
"total_misses": self._misses,
"hit_rate": self._hits / max(1, self._hits + self._misses),
"cache_fill_ratio": self._cache_used_mb / self.config.cache_capacity_mb,
"bandwidth_saved_mb": self._total_bandwidth_saved,
}
return StepResult(observation=obs, reward=reward, done=self._done, info=info)
def state(self) -> dict:
"""Return current full environment state."""
return {
"step": self._step,
"done": self._done,
"cache": {k: v.dict() for k, v in self._cache.items()},
"cache_used_mb": self._cache_used_mb,
"cache_capacity_mb": self.config.cache_capacity_mb,
"hits": self._hits,
"misses": self._misses,
"hit_rate": self._hits / max(1, self._hits + self._misses),
"bandwidth_saved_mb": self._total_bandwidth_saved,
"task": self.config.dict(),
}
# ─────────────────────────────────────────────
# Internal Logic
# ─────────────────────────────────────────────
def _process_step(
self,
action: Action,
file_id: str,
size_mb: float,
is_viral: bool,
cache_hit: bool,
) -> Reward:
hit_bonus = 0.0
eviction_penalty = 0.0
thrash_penalty = 0.0
bandwidth_saved = 0.0
wasted_penalty = 0.0
if cache_hit:
self._hits += 1
self._recent_hits.append(True)
hit_bonus = 1.0 + (0.5 if is_viral else 0.0) # viral hits worth more
bandwidth_saved = size_mb * 0.01 # normalized
self._total_bandwidth_saved += size_mb
# Update frequency
entry = self._cache[file_id]
entry.request_frequency = min(entry.request_frequency + 1, 50)
entry.last_accessed = self._step
else:
self._misses += 1
self._recent_hits.append(False)
# Try to insert new file
if self._cache_used_mb + size_mb <= self.config.cache_capacity_mb:
# Fits without eviction
self._insert_file(file_id, size_mb, is_viral)
else:
# Need to evict
if action.evict_file_id and action.evict_file_id in self._cache:
evicted = self._cache[action.evict_file_id]
# Penalize evicting high-frequency files
if evicted.request_frequency > 10:
eviction_penalty -= 0.3
if evicted.is_viral:
eviction_penalty -= 0.2
# Thrash penalty: evicted and re-requested soon
if action.evict_file_id == self._last_evicted:
thrash_penalty = -0.5
self._eviction_counts[action.evict_file_id] += 1
self._remove_file(action.evict_file_id)
self._last_evicted = action.evict_file_id
if self._cache_used_mb + size_mb <= self.config.cache_capacity_mb:
self._insert_file(file_id, size_mb, is_viral)
else:
# No valid eviction action — wasted capacity penalty
wasted_penalty = -0.2
# Wasted capacity: cache too empty when we could be caching
fill_ratio = self._cache_used_mb / self.config.cache_capacity_mb
if fill_ratio < 0.3 and self._step > 10:
wasted_penalty -= 0.1
# Keep recent_hits window at 20
if len(self._recent_hits) > 20:
self._recent_hits.pop(0)
total = hit_bonus + eviction_penalty + thrash_penalty + bandwidth_saved + wasted_penalty
return Reward(
total=round(total, 4),
cache_hit_bonus=hit_bonus,
eviction_penalty=eviction_penalty,
thrash_penalty=thrash_penalty,
bandwidth_saved=bandwidth_saved,
wasted_capacity_penalty=wasted_penalty,
)
def _insert_file(self, file_id: str, size_mb: float, is_viral: bool):
self._cache[file_id] = FileEntry(
file_id=file_id,
size_mb=size_mb,
request_frequency=1.0,
is_viral=is_viral,
last_accessed=self._step,
)
self._cache_used_mb += size_mb
def _remove_file(self, file_id: str):
if file_id in self._cache:
self._cache_used_mb -= self._cache[file_id].size_mb
self._cache_used_mb = max(0.0, self._cache_used_mb)
del self._cache[file_id]
def _make_observation(self, cache_hit: bool) -> Observation:
file_id, size_mb, is_viral = self.traffic.get_request(self._step)
preview = self.traffic.get_preview(self._step)
recent_hit_rate = (
sum(self._recent_hits) / len(self._recent_hits)
if self._recent_hits else 0.0
)
fill = self._cache_used_mb / self.config.cache_capacity_mb
return Observation(
step=self._step,
cache_used_mb=round(self._cache_used_mb, 2),
cache_capacity_mb=self.config.cache_capacity_mb,
cache_fill_ratio=round(fill, 4),
cached_files=list(self._cache.values()),
incoming_file_id=file_id,
incoming_file_size_mb=size_mb,
incoming_file_is_viral=is_viral,
cache_hit=cache_hit,
recent_hit_rate=round(recent_hit_rate, 4),
time_of_day=round(self.traffic.time_of_day(self._step), 4),
queue_preview=preview,
)
class DriftCDNEnv(CDNCacheEnv):
def __init__(self, task_id="task_hard", seed=42):
super().__init__(task_id=task_id, seed=seed)
self._original_capacity = self.config.cache_capacity_mb
self._hit_multiplier = 1.0
self._thrash_multiplier = 1.0
def reset(self):
obs = super().reset()
self.config.cache_capacity_mb = self._original_capacity
self._hit_multiplier = 1.0
self._thrash_multiplier = 1.0
return obs
def step(self, action):
self._apply_drift()
result = super().step(action)
r = result.reward
new_total = round(r.cache_hit_bonus*self._hit_multiplier + r.eviction_penalty + r.thrash_penalty*self._thrash_multiplier + r.bandwidth_saved + r.wasted_capacity_penalty, 4)
from env.models import Reward, StepResult
return StepResult(observation=result.observation, reward=Reward(total=new_total, cache_hit_bonus=r.cache_hit_bonus*self._hit_multiplier, eviction_penalty=r.eviction_penalty, thrash_penalty=r.thrash_penalty*self._thrash_multiplier, bandwidth_saved=r.bandwidth_saved, wasted_capacity_penalty=r.wasted_capacity_penalty), done=result.done, info=result.info)
def _apply_drift(self):
if self._step == 50:
self.config.cache_capacity_mb *= 0.6
self._cache_used_mb = min(self._cache_used_mb, self.config.cache_capacity_mb)
elif self._step == 100:
self.traffic.viral_ratio = min(1.0, self.traffic.viral_ratio + 0.25)
elif self._step == 150:
self._hit_multiplier = 0.6
self._thrash_multiplier = 2.5 |