Merge ~sajoupa/charm-telegraf:internal-stats into charm-telegraf:master

[Laurent Sesquès]

add the internal input plugin to base inputs, with memstats collection. Fixes lp:1895661.

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

This merge proposal is being monitored by mergebot. Change the status to Approved to merge.

[Laurent Sesquès (sajoupa)]

passed `make test`.

[Laurent Sesquès (sajoupa)]

This last commit makes memstats collection non-optional.
`make test` still passes successfully.

[Junien F (axino)]

+1

review: Approve

[Benjamin Allot (ballot)]

LGTM, you can add "-" when doing jinja (see comments), but that's not a blocker

review: Approve

[Paul Goins (vultaire)]

review: Approve

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

Change successfully merged at revision 4ef6c03cd01c7024547b7ae1d6ce1288d31733f1

diff --git a/src/templates/base_inputs.conf b/src/templates/base_inputs.conf
index 889690a..636b10e 100644
--- a/src/templates/base_inputs.conf
+++ b/src/templates/base_inputs.conf
@@ -127,6 +127,11 @@ files = ["ip_conntrack_count","ip_conntrack_max", "nf_conntrack_count","nf_connt
   # no configuration
 {% endif %}
 
+{% if "internal" not in disabled_plugins %}
+[[inputs.internal]]
+  collect_memstats = true
+{% endif %}
+
 [[inputs.exec]]
 commands = [
     "/usr/bin/awk '{ print $1 }' /proc/sys/fs/file-nr"
diff --git a/src/tests/unit/test_telegraf.py b/src/tests/unit/test_telegraf.py
index 8ef82ec..ffab0e8 100644
--- a/src/tests/unit/test_telegraf.py
+++ b/src/tests/unit/test_telegraf.py
@@ -1234,6 +1234,20 @@ def test_socket_listener_config(monkeypatch, config):
     assert expected in config_file.read()
 
 
+def test_inputs_internal_memstats(monkeypatch, config):
+    open_ports = set()
+    monkeypatch.setattr(telegraf.hookenv, "open_port", lambda p: open_ports.add(p))
+    monkeypatch.setattr(telegraf.hookenv, "close_port", lambda p: open_ports.remove(p))
+    config["disabled_plugins"] = ""  # ensure no metrics are initially disabled
+    telegraf.configure_telegraf()
+    config_file = base_dir().join("telegraf.conf")
+    expected = """
+[[inputs.internal]]
+  collect_memstats = true
+"""
+    assert expected in config_file.read()
+
+
 class TestGetHostnameLabel(unittest.TestCase):
     @patch("reactive.telegraf.get_remote_unit_name")
     @patch("charmhelpers.core.hookenv.config")