Running Varnish on Fly#

The goal: run Varnish in a Fly container as a caching proxy in front of another Fly application.

I ended up switching to Cloudflare for running a Varnish-style cache in front of my Fly application (purely to reduce the number of moving parts I needed to maintain), but I’m publishing my notes on how I got Varnish working here in case I need them in the future.

The Dockerfile#

Fly apps run Docker containers. Here’s the minimal Dockerfile that worked for me:

1
FROM varnish
2

3
COPY default.vcl /etc/varnish/
4

5
USER varnish
6

7
ENTRYPOINT [ \
8
    "varnishd", "-F", \
9
    "-f", "/etc/varnish/default.vcl", \
10
    "-a", "http=:8000,HTTP", \
11
    "-s", "malloc,256M", \
12
    "-T", "none" \
13
]

default.vcl#

The default.vcl file is the Varnish configuration file. Here’s the one I used:

1
vcl 4.1;
2

3
backend default {
4
  .host = "my-underlying-app.fly.dev";
5
  .port = "80";
6
}
7

8
sub vcl_recv {
9
    unset req.http.x-cache;
10
}
11

12
sub vcl_hit {
13
    set req.http.x-cache = "hit";
14
}
15

16
sub vcl_miss {
17
    set req.http.x-cache = "miss";
18
}
19

20
sub vcl_pass {
21
    set req.http.x-cache = "pass";
22
}
23

24
sub vcl_pipe {
25
    set req.http.x-cache = "pipe uncacheable";
26
}
27

28
sub vcl_synth {
29
    set req.http.x-cache = "synth synth";
30
    set resp.http.x-cache = req.http.x-cache;
31
}
32

33
sub vcl_deliver {
34
    if (obj.uncacheable) {
35
        set req.http.x-cache = req.http.x-cache + " uncacheable" ;
36
    } else {
37
        set req.http.x-cache = req.http.x-cache + " cached" ;
38
    }
39
    set resp.http.x-cache = req.http.x-cache;
40
}

fly.toml#

The Fly configuration file for the application:

1
app = "my-varnish-app"
2
primary_region = "lax"
3
kill_signal = "SIGINT"
4
kill_timeout = "5s"
5

6
[[services]]
7
  internal_port = 8000
8
  protocol = "tcp"
9

10
  [services.concurrency]
11
    hard_limit = 25
12
    soft_limit = 20
13

14
  [[services.ports]]
15
    handlers = ["http"]
16
    port = 80
17

18
  [[services.ports]]
19
    handlers = ["tls", "http"]
20
    port = 443
21

22
  [[services.tcp_checks]]
23
    interval = 10000
24
    timeout = 2000
25
    grace_period = "10s"

I’m using internal_port = 8000 here because I ran Varnish using -a "http=:8000,HTTP" in the ENTRYPOINT in the Dockerfile.

Deploying the application#

With all of the above files in a folder, the deploy command looks like this:

1
flyctl deploy

The result ends up running at https://my-varnish-app.fly.dev/, and will serve pages from the underlying app - only caching them if those pages include a cache-control: s-maxage=15 header or similar.

Running Varnish on Fly#

The Dockerfile#

default.vcl#

fly.toml#

Deploying the application#

Further reading#