Squid4 with SSL proxying
This dockerfile builds a Squid 4 instance and includes all the necessary
tooling to run it as a MITM (man-in-the-middle) SSL proxy.
There's a number of reasons to do this - the big one being optimizing caching
and delivery of objects during docker builds which might be downloading them
from SSL protected endpoints.
It will require you to generate your own CA and set it as trusted.
The resulting docker image uses the following configuration environment
If set, enables ICP on the given port for all users.
If set, enables HTCP on the given port for all users.
If set, tries to enable MITM SSL proxy functionality (requires CERT and KEY)
If set, the given PEM certificate is copied and used as the CA authority for
If set, the given PEM certificate is copied and used as the signing key for
the MITM CA.
Should be set to a unique value if you are chaining multiple proxy servers.
Cache size in megabytes. The cache defaults to
should mount a volume here to make it persistent.
Maximum object size to store in the cache. This is set high as one of my
typical use cases is proxying distribution images.
Default memory cache size. I've no real clue what this should be, but RAM
is plentiful so I like to keep it fairly large.
Cache peers for the squid instance may be specified with multiple CACHE_PEER
environment variables. The suffix of each is used to determine ordering by
Extra non-specific configuration lines to be appended after the main body of
the configuration file. This is a good place for custom ACL parameters.
If set to
yesthen squid configuration templating is disabled entirely, allowing
bind mounting the configuration file in manually instead. The certificate and SSL
setup still runs normally.
` If set toyes
then squid configuration templating removes allcache_dir`
lines, setting squid to memory only cache.
Allow overriding the default tls_outgoing_options supplied to OpenSSL. These
are safe defaults, but if you're in a really broken environment might not be
By default squid in SSL MITM mode treats
cache_peer entries quite differently.
Because squid unwraps the CONNECT statement when bumping an SSL connection, but
does not rewrap it when communicating with peers, it requires all peers to connect
with SSL as well. This breaks compatibility with simple minded proxies.
To work around this, proxychains-ng (
proxychains4 internally) is built and
included in this image. If you need to use an upstream proxy with a MITM
squid4, you should launch the image in proxychains mode which intercepts squids
direct outbound connections and redirects them via CONNECT requests. This also
adds SOCKS4 and SOCKS5 proxy support if so desired.
proxychains is configured with the following environment variables. As with the
CONFIG_DISABLE prevents overwriting templated files.
Default none. If set to
yesthen squid will be launched with proxychains.
You should specify some proxies when doing this.
Upstream proxies to be passed to the proxy chan config file. The suffix (
determines the order in which they are templated into the configuration file.
The format is a space separated string like "http 127.0.0.1 3129"
strict_chain. Can be
within this image. In
strict_chainmode, all proxies must be up. In
dynamic_chainmode proxies are used in order, but skipped if down.
Disable configuration and bind a configuration file to /etc/proxychains.conf
if you need more flexibility.
Default none. When set to
yes, turns on the
proxy_dnsoption for Proxychains.
In some corporate environments, its not possible to get reliable DNS outbound
proxychains-ng's DNS support won't be able to provide for Squid4
to actually work. To address this, configuration is included to setup and use
The idea of the DNS-over-HTTPS client is that it will use your local proxy and
network access to provide DNS service to Squid4.
yesthen enables and starts the DNS_OVER_HTTPS service.
127.0.0.153:53. Squid doesn't support changing the port, so keep
this in mind.
https://dns.google.com/resolve. AFAIK there's no other options for
this at the moment.
Default ``. List of DNS suffixes to not ever proxy via DNS_OVER_HTTPS.
Default ``. Normal DNS server to try resolving first against.
Default ``. Normal DNS server to try resolving last against.
Since the DNS-over-HTTPS daemon is a separate Go binary, you may also need to
specify your internal proxy as an upstream to allow it to contact the HTTPS
DNS server - do this by passing the standard
parameters. Most likely these will be the same as your
directives (and probably only the 1).
The following command line will get you up and running quickly. It presumes
you've generated a suitable CA certificate and are intending to use the proxy
as a local MITM on your machine:
sudo mkdir -p /srv/squid/cache docker run -it -p 3128:127.0.0.1:3128 --rm \ -v /srv/squid/cache:/var/cache/squid4 \ -v /etc/ssl/certs:/etc/ssl/certs:ro \ -v /etc/ssl/private/local_mitm.pem:/local-mitm.pem:ro \ -v /etc/ssl/certs/local_mitm.pem:/local-mitm.crt:ro \ -e MITM_CERT=/local-mitm.crt \ -e MITM_KEY=/local-mitm.pem \ -e MITM_PROXY=yes \ squid
Note that it doesn't really matter where we mount the certificate - the image
launch script makes a copy as root to avoid messing with permissions anyway.
Unit File for systemd
This is an example of a systemd unit file to persistly start squid4:
[Unit] Description=Squid4 Docker Container Documentation=http://wiki.squid.org After=network.target docker.service Requires=docker.service [Service] ExecStartPre=-/usr/bin/docker kill squid4 ExecStartPre=-/usr/bin/docker rm squid4 ExecStart=/usr/bin/docker run --net=host --rm \ -v /srv/squid/cache:/var/cache/squid4 \ -v /etc/ssl/certs:/etc/ssl/certs:ro \ -v /etc/ssl/private/local_mitm.pem:/local_mitm.pem:ro \ -v /etc/ssl/certs/local_mitm.pem:/local_mitm.crt:ro \ -e MITM_KEY=/local_mitm.pem \ -e MITM_CERT=/local_mitm.crt \ -e MITM_PROXY=yes \ --name squid4 \ squid [Install] WantedBy=multi-user.target