Add persistent cache volume support via CACHE_VOLUME_NAME

Mount a Modal Volume at /cache when CACHE_VOLUME_NAME is set.
Enables dependency caching across job runs for faster builds.

Author: manascb1344

DEPLOY.md

@@ -113,4 +113,5 @@ Every time a job is queued, Modal will spawn an ephemeral sandbox that runs the
 | `MAX_CONCURRENT_PER_REPO` | No | (unlimited) | Max concurrent sandboxes per repo |
 | `ALLOWED_CIDRS` | No | (allow all) | Comma-separated CIDR ranges for outbound |
 | `BLOCK_NETWORK` | No | `false` | Fully isolate sandbox network |
+| `CACHE_VOLUME_NAME` | No | - | Modal Volume name for persistent `/cache` mount |
 | `GITHUB_ENTERPRISE_DOMAIN` | No | - | Custom domain for GitHub Enterprise |

app.py

@@ -105,6 +105,8 @@ def format(self, record: logging.LogRecord) -> str:
 ALLOWED_CIDRS = [c.strip() for c in ALLOWED_CIDRS_STR.split(",") if c.strip()] if ALLOWED_CIDRS_STR else None
 BLOCK_NETWORK = os.environ.get("BLOCK_NETWORK", "").lower() in ("true", "1", "yes")
 
+CACHE_VOLUME_NAME = os.environ.get("CACHE_VOLUME_NAME", "") or None
+
 
 def _get_gpu_config(gpu_key: str):
     attr_name = GPU_LABEL_TO_ATTR.get(gpu_key)
@@ -657,6 +659,12 @@ async def github_webhook(request: Request):
                 )
                 raise HTTPException(status_code=500, detail="Internal server error")
 
+        cache_volume = None
+        sandbox_volumes = {}
+        if CACHE_VOLUME_NAME:
+            cache_volume = modal.Volume.from_name(CACHE_VOLUME_NAME, create_if_missing=True)
+            sandbox_volumes["/cache"] = cache_volume
+
         logger.info("Spawning sandbox", extra={"job_id": job_id, "repo": repo_full_name, "gpu": gpu_config is not None})
 
         cmd = (
@@ -679,6 +687,7 @@ async def github_webhook(request: Request):
             gpu=gpu_config,
             cidr_allowlist=ALLOWED_CIDRS,
             block_network=BLOCK_NETWORK,
+            volumes=sandbox_volumes,
             experimental_options={"enable_docker": True},
         )