TITLE: Feature request: Would like a way to refuse subsequent TCP connections while allowing current connections enough time to drain
This feature request was originally opened as envoyproxy/envoy#2920, but was too specific about the implementation. This issue updates the title and content to clarify the goals and be flexible about the implementation.
Given I've configured Envoy with LDS serving a TCP proxy listener on some port and there are connections in flight I would like a way to refuse subsequent TCP connections to that port while allowing current established connections to drain
We tried the following approaches, but neither of them achieve our goals:
- the LDS is updated to remove the listener
- Envoy is signalled with a
SIGTERM - Send a
GETrequest to/healthcheck/fail
write a bootstrap.yaml like
---
admin:
access_log_path: /tmp/admin_access.log
address:
socket_address:
address: 0.0.0.0
port_value: 9901
node:
id: some-envoy-node
cluster: some-envoy-cluster
dynamic_resources:
lds_config:
path: /cfg/lds-current.yaml
static_resources:
clusters:
- name: example_cluster
connect_timeout: 0.25s
type: STATIC
lb_policy: ROUND_ROBIN
hosts:
- socket_address:
address: 93.184.216.3 # IP address of example.com
port_value: 80
write a lds-current.yaml file like
version_info: "0"
resources:
- "@type": type.googleapis.com/envoy.api.v2.Listener
name: listener_0
address:
socket_address:
address: 0.0.0.0
port_value: 8080
filter_chains:
- filters:
- name: envoy.tcp_proxy
config:
stat_prefix: ingress_tcp
cluster: example_cluster
launch envoy (I'm using v1.6.0)
envoy -c /cfg/bootstrap.yaml --v2-config-only --drain-time-s 30
confirm that the TCP proxy is working
curl -v -H 'Host: example.com' 127.0.0.1:8080
next update the LDS to return an empty set of listeners. this is a two step process. first, write an empty LDS response file lds-empty.yaml
version_info: "1"
resources: []
second, move that file on top of the file being watched:
mv lds-empty.yaml lds-current.yaml
in the Envoy stdout logs you'll see a line
source/server/lds_api.cc:68] lds: remove listener 'listener_0'
attempt to connect to the port where the listener used to be:
curl -v -H 'Host: example.com' 127.0.0.1:8080
Would like to see all new TCP connections be refused immediately, as if a listener had never been added in the first place. Existing TCP connections should continue to be serviced.
the port is still open, even after the LDS update occurs
lsof -i
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
envoy 1 root 9u IPv4 30166 0t0 TCP *:9901 (LISTEN)
envoy 1 root 22u IPv4 30171 0t0 TCP *:8080 (LISTEN)
clients can connect to the port, but the TCP proxying seems to hang (can't tell where)
curl -H 'Host: example.com' -v 127.0.0.1:8080
* Rebuilt URL to: 127.0.0.1:8080/
* Trying 127.0.0.1...
* Connected to 127.0.0.1 (127.0.0.1) port 8080 (#0)
> GET / HTTP/1.1
> Host: example.com
> User-Agent: curl/7.47.0
> Accept: */*
>
^C
this state remains until --drain-time-s time has elapsed (30 seconds in this example). At that point the port is finally closed, so you see
curl 127.0.0.1:8080
curl: (7) Failed to connect to 127.0.0.1 port 8080: Connection refused
If instead of removing the listeners we signaled Envoy
pkill -SIGTERM envoy
Envoy exits immediately without allowing current connections to drain
[2018-03-28 17:42:06.995][3563][warning][main] source/server/server.cc:312] caught SIGTERM
[2018-03-28 17:42:06.995][3563][info][main] source/server/server.cc:357] main dispatch loop exited
[2018-03-28 17:42:07.004][3563][info][main] source/server/server.cc:392] exiting
Would like to see all new TCP connections be refused immediately, as if a listener had never been added in the first place. Existing TCP connections should continue to be serviced.
the port is still open, even after the LDS update occurs
lsof -i
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
envoy 1 root 9u IPv4 30166 0t0 TCP *:9901 (LISTEN)
envoy 1 root 22u IPv4 30171 0t0 TCP *:8080 (LISTEN)
clients can connect to the port, but the TCP proxying seems to hang (can't tell where)
curl -H 'Host: example.com' -v 127.0.0.1:8080
* Rebuilt URL to: 127.0.0.1:8080/
* Trying 127.0.0.1...
* Connected to 127.0.0.1 (127.0.0.1) port 8080 (#0)
> GET / HTTP/1.1
> Host: example.com
> User-Agent: curl/7.47.0
> Accept: */*
>
^C
this state remains until --drain-time-s time has elapsed (30 seconds in this example). At that point the port is finally closed, so you see
curl 127.0.0.1:8080
curl: (7) Failed to connect to 127.0.0.1 port 8080: Connection refused
In Cloud Foundry, we have the following setup currently:
Router =====> Envoy ----> App
(shared ingress) (TLS) TCP
Each application instance has a sidecar Envoy which terminates TLS connections from the shared ingress router. Applications may not speak HTTP, so we use basic TCP connectivity checks from the shared Router to the Envoy in order to infer application health and determine if a client connection should be load-balanced to that Envoy. When the upstream Envoy accepts the TCP connection, the Router considers that upstream healthy. When the upstream refuses the TCP connection, the Router considers that upstream unhealthy.
During a graceful shutdown, the scheduler ought to be able to drain the Envoy before terminating the application. This would mean that the Envoy ought to service any in-flight TCP connections without accepting any new ones.