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Last pushed: a month ago
Short Description
docker container running squid4, built with full support for MITM proxy configuration.
Full Description

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

    Default: 3128
    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
    MITM'ing connections.
    If set, the given PEM certificate is copied and used as the signing key for
    the MITM CA.
    Default: docker-squid4
    Should be set to a unique value if you are chaining multiple proxy servers.
    Default: 40000
    Cache size in megabytes. The cache defaults to /var/cache/squid4. You
    should mount a volume here to make it persistent.
    Default "1536 MB"
    Maximum object size to store in the cache. This is set high as one of my
    typical use cases is proxying distribution images.
    Default: "128 MB"
    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
    the unix sort function.
    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.
    Default no
    If set to yes then squid configuration templating is disabled entirely, allowing
    bind mounting the configuration file in manually instead. The certificate and SSL
    setup still runs normally.
    Default ` If set toyesthen squid configuration templating removes allcache_dir`
    lines, setting squid to memory only cache.
    Default NO_SSLv3,NO_TLSv1
    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
others above, CONFIG_DISABLE prevents overwriting templated files.

    Default none. If set to yes then 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 (x)
    determines the order in which they are templated into the configuration file.
    The format is a space separated string like "http 3129"
    Default strict_chain. Can be strict_chain or dynamic_chain sensibly
    within this image. In strict_chain mode, all proxies must be up. In
    dynamic_chain mode 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_dns option for Proxychains.


In some corporate environments, its not possible to get reliable DNS outbound
service and 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.

    Default no. If yes then enables and starts the DNS_OVER_HTTPS service.
    Default Squid doesn't support changing the port, so keep
    this in mind.
    Default 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 http_proxy and https_proxy
parameters. Most likely these will be the same as your PROXYCHAIN_PROXYx
directives (and probably only the 1).

Example Usage

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: --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 \

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:

Description=Squid4 Docker Container
Documentation= docker.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 \

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