Add blogs folder for blog post code (GoogleCloudPlatform#5360)

* Add `blogs` folder for blog post code

* fix lint

* add apache license to YAML files

* Add list_buckets_result task, change project

* refactor to use variables and xcoms

* add fixture to initialize airflow db

* replace project string with placeholder

* fix lint

Author: leahecole

composer/blog/README.md

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+# Cloud Composer Blog Posts
+
+Beginning in 2021, any code samples written by Cloud Composer DevRel and featured in blog posts are found in this repo. 

composer/blog/__init__.py

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+# GCP Tech Blog
+The code here is featured in posts found on the [Google Cloud Platform Tech Blog](https://cloud.google.com/blog/topics/developers-practitioners)

composer/blog/gcp-tech-blog/README.md

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+# Copyright 2021 Google LLC
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     https://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+FROM python:3.8
+
+# Allow statements and log messages to immediately appear in the Cloud Run logs
+ENV PYTHONUNBUFFERED True
+
+COPY requirements.txt ./
+COPY requirements-composer.txt ./
+COPY requirements-test.txt ./
+
+RUN pip install --no-cache-dir -r requirements.txt
+RUN pip install --no-cache-dir -r requirements-test.txt
+RUN pip install --no-cache-dir -r requirements-composer.txt
+
+#copy dag code to container image
+ENV DAGS /dags
+WORKDIR $DAGS
+COPY . ./
+CMD ["pytest", "-s", "dags/example_dag_test.py"]

composer/blog/gcp-tech-blog/__init__.py

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+# Copyright 2021 Google LLC
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     https://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import uuid
+
+from airflow import models
+
+from airflow.operators.bash_operator import BashOperator
+from airflow.operators.python_operator import PythonOperator
+from airflow.providers.google.cloud.operators.gcs import GCSCreateBucketOperator
+from airflow.providers.google.cloud.operators.gcs import GCSDeleteBucketOperator
+from airflow.providers.google.cloud.operators.gcs import GCSListObjectsOperator
+
+from airflow.utils.dates import days_ago
+from airflow.utils.state import State
+
+# Assumes existence of Airflow Variable set to name of GCP Project
+PROJECT_ID = models.Variable.get("gcp_project")
+
+
+with models.DAG(
+    "example_gcs",
+    start_date=days_ago(1),
+    schedule_interval=None,
+) as dag:
+    generate_uuid = PythonOperator(
+        task_id='generate_uuid',
+        python_callable=lambda: str(uuid.uuid4())
+    )
+    create_bucket = GCSCreateBucketOperator(task_id="create_bucket", bucket_name="{{ task_instance.xcom_pull('generate_uuid') }}", project_id=PROJECT_ID)
+    list_objects = GCSListObjectsOperator(task_id="list_objects", bucket="{{ task_instance.xcom_pull('generate_uuid') }}")
+    list_buckets_result = BashOperator(
+        task_id="list_buckets_result",
+        bash_command="echo \"{{ task_instance.xcom_pull('list_objects') }}\"",
+    )
+    delete_bucket = GCSDeleteBucketOperator(task_id="delete_bucket", bucket_name="{{ task_instance.xcom_pull('generate_uuid') }}")
+
+    generate_uuid >> create_bucket >> list_objects >> list_buckets_result >> delete_bucket
+
+
+if __name__ == "__main__":
+    dag.clear(dag_run_state=State.NONE)
+    dag.run()

composer/blog/gcp-tech-blog/unit-test-dags-cloud-build/Dockerfile

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+# Copyright 2021 Google LLC
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     https://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from airflow import models
+import airflow.utils.db
+import internal_unit_testing
+import pytest
+
+# user should substitute their project ID
+PROJECT_ID = 'your-project-id'
+
+
+@pytest.fixture(autouse=True, scope="module")
+def initalize_airflow_database():
+    airflow.utils.db.initdb()
+
+
+def test_dag_import():
+    models.Variable.set('gcp_project', PROJECT_ID)
+    from . import example_dag
+    internal_unit_testing.assert_has_valid_dag(example_dag)

composer/blog/gcp-tech-blog/unit-test-dags-cloud-build/__init__.py

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+{
+  "extends": [
+    "config:base"
+  ],
+  "baseBranches": ["main"],
+  "masterIssue": true,
+  "pip_requirements": {
+    "fileMatch": ["requirements-composer.txt"]
+  }
+}