From 390a4d55102f49cade830bf422ebf36e3be7dacb Mon Sep 17 00:00:00 2001
From: Bert Blommers <info@bertblommers.nl>
Date: Sun, 8 Nov 2020 14:18:49 +0000
Subject: [PATCH] #3359 - Only initiate Docker when invoking Lambdas

---
 moto/awslambda/models.py | 38 +++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 15 deletions(-)

diff --git a/moto/awslambda/models.py b/moto/awslambda/models.py
index ce9c78fc6..12f98ec0c 100644
--- a/moto/awslambda/models.py
+++ b/moto/awslambda/models.py
@@ -162,25 +162,11 @@ class LambdaFunction(CloudFormationModel):
         self.run_time = spec["Runtime"]
         self.logs_backend = logs_backends[self.region]
         self.environment_vars = spec.get("Environment", {}).get("Variables", {})
-        self.docker_client = docker.from_env()
+        self.docker_client = None
         self.policy = None
         self.state = "Active"
         self.reserved_concurrency = spec.get("ReservedConcurrentExecutions", None)
 
-        # Unfortunately mocking replaces this method w/o fallback enabled, so we
-        # need to replace it if we detect it's been mocked
-        if requests.adapters.HTTPAdapter.send != _orig_adapter_send:
-            _orig_get_adapter = self.docker_client.api.get_adapter
-
-            def replace_adapter_send(*args, **kwargs):
-                adapter = _orig_get_adapter(*args, **kwargs)
-
-                if isinstance(adapter, requests.adapters.HTTPAdapter):
-                    adapter.send = functools.partial(_orig_adapter_send, adapter)
-                return adapter
-
-            self.docker_client.api.get_adapter = replace_adapter_send
-
         # optional
         self.description = spec.get("Description", "")
         self.memory_size = spec.get("MemorySize", 128)
@@ -242,6 +228,26 @@ class LambdaFunction(CloudFormationModel):
 
         self.tags = dict()
 
+    def initiate_docker_client(self):
+        # We should only initiate the Docker Client at runtime.
+        # The docker.from_env() call will fall if Docker is not running
+        if self.docker_client is None:
+            self.docker_client = docker.from_env()
+
+            # Unfortunately mocking replaces this method w/o fallback enabled, so we
+            # need to replace it if we detect it's been mocked
+            if requests.adapters.HTTPAdapter.send != _orig_adapter_send:
+                _orig_get_adapter = self.docker_client.api.get_adapter
+
+                def replace_adapter_send(*args, **kwargs):
+                    adapter = _orig_get_adapter(*args, **kwargs)
+
+                    if isinstance(adapter, requests.adapters.HTTPAdapter):
+                        adapter.send = functools.partial(_orig_adapter_send, adapter)
+                    return adapter
+
+                self.docker_client.api.get_adapter = replace_adapter_send
+
     def set_version(self, version):
         self.function_arn = make_function_ver_arn(
             self.region, ACCOUNT_ID, self.function_name, version
@@ -412,6 +418,8 @@ class LambdaFunction(CloudFormationModel):
 
             env_vars.update(self.environment_vars)
 
+            self.initiate_docker_client()
+
             container = exit_code = None
             log_config = docker.types.LogConfig(type=docker.types.LogConfig.types.JSON)
             with _DockerDataVolumeContext(self) as data_vol: