make --fast robust against credential or wheel updates

sky/backends/backend.py

@@ -45,20 +45,45 @@ def check_resources_fit_cluster(self, handle: _ResourceHandleType,
     @timeline.event
     @usage_lib.messages.usage.update_runtime('provision')
     def provision(
-            self,
-            task: 'task_lib.Task',
-            to_provision: Optional['resources.Resources'],
-            dryrun: bool,
-            stream_logs: bool,
-            cluster_name: Optional[str] = None,
-            retry_until_up: bool = False) -> Optional[_ResourceHandleType]:
+        self,
+        task: 'task_lib.Task',
+        to_provision: Optional['resources.Resources'],
+        dryrun: bool,
+        stream_logs: bool,
+        cluster_name: Optional[str] = None,
+        retry_until_up: bool = False,
+        skip_if_no_cluster_updates: bool = False,
+    ) -> Optional[_ResourceHandleType]:
+        """Provisions resources for the given task.
+
+        Args:
+            task: The task to provision resources for.
+            to_provision: Resource config to provision. Should only be None if
+                cluster_name refers to an existing cluster, whose resources will
+                be used.
+            dryrun: If True, don't actually provision anything.
+            stream_logs: If True, stream provisioning logs to console.
+            cluster_name: Name of the cluster to provision. If None, a name will
+                be auto-generated. If the name refers to an existing cluster,
+                the existing cluster will be reused and re-provisioned.
+            retry_until_up: If True, retry provisioning until resources are
+                successfully launched.
+            skip_if_no_cluster_updates: If True, calculate the cluster config
+                and compare to the existing cluster_name's config. Skip
+                provisioning if no updates are needed for the existing cluster.
+
+        Returns:
+            A ResourceHandle object for the provisioned resources, or None if
+            dryrun is True.
+        """
         if cluster_name is None:
             cluster_name = sky.backends.backend_utils.generate_cluster_name()
         usage_lib.record_cluster_name_for_current_operation(cluster_name)
         usage_lib.messages.usage.update_actual_task(task)
         with rich_utils.safe_status(ux_utils.spinner_message('Launching')):
             return self._provision(task, to_provision, dryrun, stream_logs,
-                                   cluster_name, retry_until_up)
+                                   cluster_name, retry_until_up,
+                                   skip_if_no_cluster_updates)
 
     @timeline.event
     @usage_lib.messages.usage.update_runtime('sync_workdir')
@@ -126,13 +151,15 @@ def register_info(self, **kwargs) -> None:
 
     # --- Implementations of the APIs ---
     def _provision(
-            self,
-            task: 'task_lib.Task',
-            to_provision: Optional['resources.Resources'],
-            dryrun: bool,
-            stream_logs: bool,
-            cluster_name: str,
-            retry_until_up: bool = False) -> Optional[_ResourceHandleType]:
+        self,
+        task: 'task_lib.Task',
+        to_provision: Optional['resources.Resources'],
+        dryrun: bool,
+        stream_logs: bool,
+        cluster_name: str,
+        retry_until_up: bool = False,
+        skip_if_no_cluster_updates: bool = False,
+    ) -> Optional[_ResourceHandleType]:
         raise NotImplementedError
 
     def _sync_workdir(self, handle: _ResourceHandleType, workdir: Path) -> None:

sky/backends/backend_utils.py

@@ -3,6 +3,7 @@
 import enum
 import fnmatch
 import functools
+import hashlib
 import os
 import pathlib
 import pprint
@@ -640,11 +641,14 @@ def write_cluster_config(
         keep_launch_fields_in_existing_config: bool = True) -> Dict[str, str]:
     """Fills in cluster configuration templates and writes them out.
 
-    Returns: {provisioner: path to yaml, the provisioning spec}.
-      'provisioner' can be
-        - 'ray'
-        - 'tpu-create-script' (if TPU is requested)
-        - 'tpu-delete-script' (if TPU is requested)
+    Returns:
+        Dict with the following keys:
+        - 'ray': Path to the generated Ray yaml config file
+        - 'cluster_name': Name of the cluster
+        - 'cluster_name_on_cloud': Name of the cluster as it appears in the
+          cloud provider
+        - 'config_hash': Hash of the cluster config and file mounts contents
+
     Raises:
         exceptions.ResourcesUnavailableError: if the region/zones requested does
             not appear in the catalog, or an ssh_proxy_command is specified but
@@ -860,6 +864,7 @@ def write_cluster_config(
     if dryrun:
         # If dryrun, return the unfinished tmp yaml path.
         config_dict['ray'] = tmp_yaml_path
+        config_dict['config_hash'] = _deterministic_yaml_hash(tmp_yaml_path)
         return config_dict
     _add_auth_to_cluster_config(cloud, tmp_yaml_path)
 
@@ -882,6 +887,11 @@ def write_cluster_config(
     yaml_config = common_utils.read_yaml(tmp_yaml_path)
     config_dict['cluster_name_on_cloud'] = yaml_config['cluster_name']
 
+    # Make sure to do this before we optimize file mounts. Optimization is
+    # non-deterministic, but everything else before this point should be
+    # deterministic.
+    config_dict['config_hash'] = _deterministic_yaml_hash(tmp_yaml_path)
+
     # Optimization: copy the contents of source files in file_mounts to a
     # special dir, and upload that as the only file_mount instead. Delay
     # calling this optimization until now, when all source files have been
@@ -990,6 +1000,115 @@ def get_ready_nodes_counts(pattern, output):
     return ready_head, ready_workers
 
 
+@timeline.event
+def _deterministic_yaml_hash(yaml_path: str) -> str:
+    """Hash the cluster yaml and contents of file mounts to a unique string.
+
+    Two invocations of this function should return the same string if and only
+    if the contents of the yaml are the same and the file contents of all the
+    file_mounts specified in the yaml are the same.
+
+    Limitations:
+    - This function can be expensive if the file mounts are large. (E.g. a few
+      seconds for ~1GB.) This should be okay since we expect that the
+      file_mounts in the cluster yaml (the wheel and cloud credentials) will be
+      small.
+    - Symbolic links are not explicitly handled. Some symbolic link changes may
+      not be detected.
+
+    Implementation: We create a byte sequence that captures the state of the
+    yaml file and all the files in the file mounts, then hash the byte sequence.
+
+    The format of the byte sequence is:
+    32 bytes - sha256 hash of the yaml file
+    for each file mount:
+      file mount remote destination (UTF-8), \0
+      if the file mount source is a file:
+        'file' encoded to UTF-8
+        32 byte sha256 hash of the file contents
+      if the file mount source is a directory:
+        'dir' encoded to UTF-8
+        for each directory and subdirectory withinin the file mount (starting from
+            the root and descending recursively):
+          name of the directory (UTF-8), \0
+          name of each subdirectory within the directory (UTF-8) terminated by \0
+          \0
+          for each file in the directory:
+            name of the file (UTF-8), \0
+            32 bytes - sha256 hash of the file contents
+          \0
+      if the file mount source is something else or does not exist, nothing
+      \0\0
+
+    Rather than constructing the whole byte sequence, which may be quite large,
+    we construct it incrementally by using hash.update() to add new bytes.
+    """
+
+    def _hash_file(path: str) -> bytes:
+        return common_utils.hash_file(path, 'sha256').digest()
+
+    config_hash = hashlib.sha256()
+
+    config_hash.update(_hash_file(yaml_path))
+
+    yaml_config = common_utils.read_yaml(yaml_path)
+    file_mounts = yaml_config.get('file_mounts', {})
+    # Remove the file mounts added by the newline.
+    if '' in file_mounts:
+        assert file_mounts[''] == '', file_mounts['']
+        file_mounts.pop('')
+
+    for dst, src in sorted(file_mounts.items()):
+        expanded_src = os.path.expanduser(src)
+        config_hash.update(dst.encode('utf-8') + b'\0')
+
+        # If the file mount source is a symlink, this should be true. In that
+        # case we hash the contents of the symlink destination.
+        if os.path.isfile(expanded_src):
+            config_hash.update('file'.encode('utf-8'))
+            config_hash.update(_hash_file(expanded_src))
+
+        # This can also be a symlink to a directory. os.walk will treat it as a
+        # normal directory and list the contents of the symlink destination.
+        elif os.path.isdir(expanded_src):
+            config_hash.update('dir'.encode('utf-8'))
+
+            # Aside from expanded_src, os.walk will list symlinks to directories
+            # but will not recurse into them.
+            for (dirpath, dirnames, filenames) in os.walk(expanded_src):
+                config_hash.update(dirpath.encode('utf-8') + b'\0')
+
+                # Note: inplace sort will also affect the traversal order of
+                # os.walk. We need it so that the os.walk order is
+                # deterministic.
+                dirnames.sort()
+                # This includes symlinks to directories. os.walk will recurse
+                # into all the directories but not the symlinks. We don't hash
+                # the link destination, so if a symlink to a directory changes,
+                # we won't notice.
+                for dirname in dirnames:
+                    config_hash.update(dirname.encode('utf-8') + b'\0')
+                config_hash.update(b'\0')
+
+                filenames.sort()
+                # This includes symlinks to files. We could hash the symlink
+                # destination itself but instead just hash the destination
+                # contents.
+                for filename in filenames:
+                    config_hash.update(filename.encode('utf-8') + b'\0')
+                    config_hash.update(
+                        _hash_file(os.path.join(dirpath, filename)))
+                config_hash.update(b'\0')
+
+        else:
+            logger.debug(
+                f'Unexpected file_mount that is not a file or dir: {src}')
+
+        config_hash.update(b'\0\0')
+
+    return config_hash.hexdigest()
+
+
 def get_docker_user(ip: str, cluster_config_file: str) -> str:
     """Find docker container username."""
     ssh_credentials = ssh_credential_from_yaml(cluster_config_file)