Merge ~pjdc/ubuntu-mirror-charm/+git/ubuntu-mirror-charm:skip-network-sysctls-in-lxc into ubuntu-mirror-charm:master

[Paul Collins]

skip sysctl keys that break container deployments when in a container

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

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

[Haw Loeung (hloeung)]

LGTM

review: Approve (+1)

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

Change successfully merged at revision 12f1c7d22943796a1e40db80dcd81730f39db99a

diff --git a/hooks/hooks.py b/hooks/hooks.py
index eb335cb..8b47b2c 100755
--- a/hooks/hooks.py
+++ b/hooks/hooks.py
@@ -709,20 +709,41 @@ def configure_extra_mirrors():
             relation_set(r, encoded)
 
 
+# https://discuss.linuxcontainers.org/t/how-to-detect-lxd-from-inside-container/6042
+def is_lxc():
+    if os.getuid() != 0:
+        raise Exception('is_lxc: cannot detect lxd - not running as root')
+
+    if 'container=lxc' in open('/proc/1/environ').read().split('\0'):
+        return True
+
+    return False
+
+
 def configure_sysctl():
-    sysctl_settings = {
+    # In a container, these keys exist but can't be changed.  sysctl
+    # seems to realize that if setting these fail as root, something
+    # is beyond our control and exits 0.  Only add such keys here.
+    general_settings = {
         # We now run with 32k apache_max_clients, fix issue with thread creation
         # https://publib.boulder.ibm.com/httpserv/ihsdiag/apr_thread_create.html
         'kernel.pid_max': 65536,
+        # RT#90964: Kill swap on ubuntu-archive servers
+        'vm.swappiness': 0,
+    }
+    sysctl.create(yaml.dump(general_settings), '/etc/sysctl.d/90-ubuntu-mirror.conf')
+
+    # net.core and net.ipv6.route are empty in containers.  sysctl
+    # exits 255 for nonexistent keys, so don't even bother trying.
+    non_container_settings = {
         # RT#102466: BBR congestion control
         'net.core.default_qdisc': 'fq',
         'net.ipv4.tcp_congestion_control': 'bbr',
         # RT#68166: Tune kernel for larger number of IPv6 users
         'net.ipv6.route.max_size': 16384,
-        # RT#90964: Kill swap on ubuntu-archive servers
-        'vm.swappiness': 0,
     }
-    sysctl.create(yaml.dump(sysctl_settings), '/etc/sysctl.d/90-ubuntu-mirror.conf')
+    if not is_lxc():
+        sysctl.create(yaml.dump(non_container_settings), '/etc/sysctl.d/90-ubuntu-mirror-non-container.conf')
 
 
 def configure_user():