From b85051633ee2b5132b058b9187762ddaa958a3b2 Mon Sep 17 00:00:00 2001
From: William Schroeder <wschroeder@gmail.com>
Date: Wed, 29 Dec 2021 11:36:12 -0600
Subject: [PATCH 1/2] Some applications do not start supervisor children
 (CRITICAL)

This code filters out children that are not supervisors so we can avoid
crashing remote processes that do not handle the which_children message.

I marked this as critical, as monitoring should not crash remote
systems.
---
 apps/epl_st/src/epl_st.erl | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/apps/epl_st/src/epl_st.erl b/apps/epl_st/src/epl_st.erl
index 53fa81b..51afd1c 100644
--- a/apps/epl_st/src/epl_st.erl
+++ b/apps/epl_st/src/epl_st.erl
@@ -92,6 +92,9 @@ code_change(_OldVsn, State, _Extra) ->
 %%% Internal functions
 %%%===================================================================
 
+is_supervisor(Pid) ->
+    element(1, proc_lib:initial_call(Pid)) == supervisor.
+
 generate_sup_tree({_Name, Pid, worker, _Mods}) ->
     worker_node(Pid);
 generate_sup_tree({_Name, Pid, supervisor, _Mods}) ->
@@ -101,7 +104,11 @@ generate_sup_tree(undefined) ->
     #{};
 generate_sup_tree(MasterPid) ->
     {SupPid, _SupName} = command(fun application_master:get_child/1, [MasterPid]),
-    Children = command(fun supervisor:which_children/1, [SupPid]),
+    IsSupervisor = is_supervisor(SupPid),
+    Children = if
+        IsSupervisor -> command(fun supervisor:which_children/1, [SupPid]);
+        true         -> []
+    end,
     sup_node(SupPid, generate_children(Children)).
 
 generate_children(Children) ->

From 719cbd481dd7d64fee47756949491d5f67ae661a Mon Sep 17 00:00:00 2001
From: William Schroeder <wschroeder@gmail.com>
Date: Wed, 29 Dec 2021 11:39:01 -0600
Subject: [PATCH 2/2] More safely handle race condition of ETS tables vanishing
 mid-query

The time between ets:all/0 and the series of ets:info/1 is enough time
for tables that exist in ets:all/0's output to vanish in systems with
temporary process trees. This code filters out the caught crashes due to
the tables not existing.
---
 apps/epl_ets/src/epl_ets_metric.erl | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/apps/epl_ets/src/epl_ets_metric.erl b/apps/epl_ets/src/epl_ets_metric.erl
index 41eadab..53b6bce 100644
--- a/apps/epl_ets/src/epl_ets_metric.erl
+++ b/apps/epl_ets/src/epl_ets_metric.erl
@@ -96,8 +96,11 @@ calculate_memory_percent(MemoryData) ->
 
 get_ets_info(Node, Tab) ->
     {ok, Info}  = epl:command(Node, fun ets:info/1, [Tab]),
-    InfoMap = proplist_to_map(Info),
-    {Tab, InfoMap}.
+    if
+        Info == undefined -> {Tab, #{}};
+        true              -> InfoMap = proplist_to_map(Info),
+                             {Tab, InfoMap}
+    end.
 
 transform_traces_by_pid(Traces) ->
     TracesByPid = split_traces_by_pid(Traces),
@@ -211,6 +214,9 @@ namify_val(Val) ->
 namify(Name) ->
     epl_viz_map:namify(Name).
 
+
+proplist_to_map({'EXIT', _reason}) -> #{};
+
 proplist_to_map(Proplist) ->
     lists:foldl(fun({Prop, Val}, Map) -> maps:put(namify(Prop), namify_val(Val), 
                                                   Map) end, #{}, Proplist).