Resolve circular import and other improvements

* Build app from factory
* Add development dependencies
* Improve static type annotations for dns logic
* Remove explicit class references
* Make the views object a blueprint
* Indirect app reference via flask.current_app
* Use built-in logger
* Fix import in runner
* Gitignore tags, .env
* Add tags, outdated as make targets

Author: fionn

.gitignore

@@ -2,5 +2,6 @@
 *.pdf
 __pycache__/
 .mypy_cache/
-aws_credentials.sh
 venv/
+.env
+tags

Makefile

@@ -1,11 +1,21 @@
-venv: requirements.txt
+VIRTUAL_ENV ?= venv
+SRC = app/
+
+venv: requirements.txt requirements_dev.txt
 	@python3 -m venv $@
-	@source $@/bin/activate && pip install -r $<
+	@source $@/bin/activate && pip install -r $< -r requirements_dev.txt
+
+tags: $(SRC)
+	@ctags --languages=python --python-kinds=-i -R $(SRC)
+
+.PHONY: outdated
+outdated:
+	@(source $(VIRTUAL_ENV)/bin/activate && pip list --outdated)
 
 .PHONY: lint
 lint:
-	@pylint -f colorized app/
+	@pylint -f colorized $(SRC)
 
 .PHONY: typecheck
 typecheck:
-	@mypy app/
+	@mypy $(SRC)

Procfile

@@ -1 +1 @@
-web: gunicorn app:app --preload --log-file=-
+web: gunicorn "app:create_app()" --preload --log-file=-

app/__init__.py

@@ -1,5 +1,18 @@
 """App"""
+
+import os
+
 from flask import Flask
 
-app = Flask(__name__)
-from app import views
+def create_app() -> Flask:
+    """app factory"""
+    app = Flask(__name__)
+    app.secret_key = os.environ["SECRET_KEY"]
+
+    with app.app_context():
+        # We import here because views uses flask.current_app to avoid a
+        # circular import
+        from .views import BP as views_bp
+        app.register_blueprint(views_bp)
+
+    return app

app/dns/dns.py

@@ -2,6 +2,7 @@
 """DNS logic"""
 
 import os
+from typing import List
 
 import boto
 import route53 # type: ignore
@@ -12,13 +13,13 @@
 # pylint: disable=too-few-public-methods
 class Cluster():
     """A class for cluster objects"""
-    instances: list = []
-    records: list = []
-    zone = None
+    instances: List["Cluster"] = []
+    records: List["route53.resource_record_set.AResourceRecordSet"] = []
+    zone: "route53.hosted_zone.HostedZone" = None
     n = 4 # Number of unique clusters
 
     def __init__(self, cluster_id: int) -> None:
-        self.__class__.instances.append(self)
+        self.instances.append(self)
         self.cluster_id = cluster_id
         self.cluster_name = self._name()
         self.subdomain = self._subdomain()
@@ -47,21 +48,21 @@ class Server(Cluster):
 
     def __init__(self, cluster_id: int, friendly_name: str) -> None:
         super().__init__(cluster_id)
-        self.server_id = len(self.__class__.instances)
+        self.server_id = len(self.instances)
         self.friendly_name = friendly_name
         self.ip_string = "0.0.0.0"
         self.dns = "NONE"
 
     def add_to_rotation(self) -> None:
         """Adds the server's IP to the cluster's subdomain."""
-        fqdn = self.subdomain + "." + self.__class__.zone.name
+        fqdn = self.subdomain + "." + self.zone.name
 
         # If records could simply be added & removed, this would make the
         # UI behave better with synchronous post requests.
         # Instead we have to rewrite the whole record.
 
         ips: list = []
-        for record in self.__class__.records:
+        for record in self.records:
             if fqdn == record.name:
                 ips = record.records[:]
                 break
@@ -72,7 +73,7 @@ def add_to_rotation(self) -> None:
                                     aws_secret_access_key=AWS_ACCESS_SECRET)
 
         changes = boto.route53.record.ResourceRecordSets(conn, # type: ignore
-                                                         self.__class__.zone.id)
+                                                         self.zone.id)
         change = changes.add_change("UPSERT", fqdn, "A")
 
         for ip_address in set(ips):
@@ -82,10 +83,10 @@ def add_to_rotation(self) -> None:
 
     def remove_from_rotation(self) -> None:
         """Removes the server's IP from the DNS record."""
-        fqdn = self.subdomain + "." + self.__class__.zone.name
+        fqdn = self.subdomain + "." + self.zone.name
 
         ips: list = []
-        for record in self.__class__.records:
+        for record in self.records:
             if fqdn == record.name:
                 ips = record.records[:]
                 break
@@ -99,7 +100,7 @@ def remove_from_rotation(self) -> None:
                                     aws_secret_access_key=AWS_ACCESS_SECRET)
 
         changes = boto.route53.record.ResourceRecordSets(conn, # type: ignore
-                                                         self.__class__.zone.id)
+                                                         self.zone.id)
 
         # This should be simple, but seemingly the API complains unless
         # it's updated in this arduous fashion.
@@ -124,8 +125,9 @@ def dns() -> list:
 
     zone = list(conn.list_hosted_zones())[0]
     records = [record for record in zone.record_sets]
-    records = list(filter(lambda x: x.rrset_type == "A", records))
-    records = list(filter(lambda x: x.name != zone.name, records))
+
+    records = [r for r in zone.record_sets \
+               if (r.rrset_type == "A" and r.name != zone.name)]
 
     Cluster.zone = zone
     Cluster.records = records
@@ -172,7 +174,7 @@ def print_servers() -> None:
 
 def print_dns(dns_records: list) -> None:
     """ASCII analogy of the DNS UI."""
-    print("\n\033[1mDomain\t\t\t IP(s)\t\t Server(s)\t Cluster\033[0m")
+    print("\n\033[1mDomain\t\t\t\t\t IP(s)\t\t Server(s)\t Cluster\033[0m")
     for record in dns_records:
         matching_servers = []
         for server in Server.instances:

app/views.py

@@ -1,42 +1,43 @@
-"""flask views object"""
+"""Blueprint for views"""
 
 import flask
 import werkzeug
-from app import app
 from .dns.dns import Cluster, Server, dns, update_server_dns, create_instances
 
-app.secret_key = "lQq8UJPnzpqWpKAIE0PrC0tddlWGXXuBVHwbtks65j0="
+BP = flask.Blueprint("views", __name__, url_prefix="/")
 
-@app.route("/")
-@app.route("/index")
+APP = flask.current_app
+
+@APP.route("/")
+@APP.route("/index")
 def index() -> flask.signals.template_rendered:
     """index"""
     links = [
         {
-            'title': 'Currently published DNS entries',
-            'url': 'dns'
+            "title": "Currently published DNS entries",
+            "url": "dns"
         },
         {
-            'title': 'Servers',
-            'url': 'servers'
+            "title": "Servers",
+            "url": "servers"
         }
     ]
     return flask.render_template("index.html", title="Home", links=links)
 
-@app.route("/servers")
+@APP.route("/servers")
 def servers_ui() -> flask.signals.template_rendered:
     """renders the server UI"""
     update_server_dns(dns())
     servers = Server.instances
     return flask.render_template("servers.html", title="Servers", servers=servers)
 
-@app.route("/dns")
+@APP.route("/dns")
 def dns_ui() -> flask.signals.template_rendered:
     """renders the DNS UI"""
     return flask.render_template("dns.html", title="DNS", zone=Cluster.zone,
                                  servers=Server.instances, dns_records=dns())
 
-@app.route("/rotate", methods=["GET", "POST"])
+@APP.route("/rotate", methods=["GET", "POST"])
 def rotate() -> werkzeug.wrappers.Response:
     """ Moves the server(s) into / out of DNS rotation """
     if flask.request.method == "POST":
@@ -49,13 +50,13 @@ def rotate() -> werkzeug.wrappers.Response:
                     flask.flash("Added server " + server.friendly_name + \
                                 " to DNS A record " + server.subdomain + \
                                 "." + server.zone.name)
-                    print("add", server.friendly_name)
+                    APP.logger.info("add %s", server.friendly_name)
                     server.add_to_rotation()
                 elif action == "remove":
                     flask.flash("Removed server " + server.friendly_name + \
                                 " from DNS A record " + server.subdomain + \
                                 "." + server.zone.name)
-                    print("remove", server.friendly_name)
+                    APP.logger.info("remove %s", server.friendly_name)
                     server.remove_from_rotation()
                 break
 

requirements_dev.txt

@@ -0,0 +1,3 @@
+mypy >= 0.670
+pylint >= 2.3.1
+python-dotenv >= 0.10.1

run.py

@@ -1,7 +1,12 @@
 #!/usr/bin/env python3
 """dns_automator runner"""
 
-from app import app
+from app import create_app
 
-if __name__ == "__main__":
+def main() -> None:
+    """Entry point"""
+    app = create_app()
     app.run(debug=True)
+
+if __name__ == "__main__":
+    main()