Ensure python3 executable is available on cluster (#334)

* ensure python3 is available on cluster

* add change log

* change log wording

CHANGES.md

@@ -18,9 +18,11 @@
 
 * [#311]: Changed how Flintrock manages its own security groups to reduce the likelihood of hitting any limits on the number of rules per security group.
 * [#329]: Dropped support for Python 3.5 and added automated testing for Python 3.8 and 3.9.
+* [#334]: Flintrock now ensures that `python3` is available on launched clusters and sets that as the default Python that PySpark will use.
 
 [#311]: https://github.com/nchammas/flintrock/pull/311
 [#329]: https://github.com/nchammas/flintrock/pull/329
+[#334]: https://github.com/nchammas/flintrock/pull/334
 
 ## [1.0.0] - 2020-01-11
 

flintrock/core.py

@@ -666,6 +666,17 @@ def setup_node(
     cluster.storage_dirs.root = storage_dirs['root']
     cluster.storage_dirs.ephemeral = storage_dirs['ephemeral']
 
+    # TODO: Move Python and Java setup to new service under services.py.
+    #       New service to cover Python/Scala/Java: LanguageRuntimes (name?)
+    ssh_check_output(
+        client=ssh_client,
+        command=(
+            """
+            set -e
+            sudo yum install -y python3
+            """
+        )
+    )
     ensure_java(ssh_client, java_version)
 
     for service in services:

flintrock/templates/spark/conf/spark-env.sh

@@ -20,3 +20,6 @@ export SPARK_PUBLIC_DNS="$(curl --silent http://169.254.169.254/latest/meta-data
 # Need to find a way to do this, since "sudo ulimit..." doesn't fly.
 # Probably need to edit some Linux config file.
 # ulimit -n 1000000
+
+# Should this be made part of a Python service somehow?
+export PYSPARK_PYTHON="python3"