Handle jump not being installed in code

.github/workflows/beeper-ci.yml

@@ -35,7 +35,6 @@ jobs:
       - uses: actions/setup-python@v2
       - run: pip install poetry
       - run: poetry install --extras all
-      - run: poetry run pip install jump-consistent-hash
       - run: poetry run trial -j4 tests
 
   test-sytest:

synapse/replication/tcp/external_sharded_cache.py

@@ -18,7 +18,6 @@
 from collections import defaultdict
 from typing import TYPE_CHECKING, Any, Callable, Coroutine, Dict, List, Optional, Union
 
-import jump
 from prometheus_client import Counter, Histogram
 from txredisapi import ConnectionError, ConnectionHandler, RedisError
 
@@ -32,6 +31,13 @@
 if TYPE_CHECKING:
     from synapse.server import HomeServer
 
+try:
+    import jump
+except ImportError:
+    has_jump = False
+else:
+    has_jump = True
+
 set_counter = Counter(
     "synapse_external_sharded_cache_set",
     "Number of times we set a cache",
@@ -82,6 +88,10 @@ def __init__(self, hs: "HomeServer"):
         self._reactor = hs.get_reactor()
 
         if hs.config.redis.redis_enabled and hs.config.redis.cache_shard_hosts:
+            if not has_jump:
+                logger.error("Cannot start sharded cache, jump module not found!")
+                return
+
             for shard in hs.config.redis.cache_shard_hosts:
                 logger.info(
                     "Connecting to redis (host=%r port=%r) for external cache",