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Update docs of containers.conf configs affecting /etc/hosts #2184

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Oct 4, 2024
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Update docs of containers.conf configs affecting /etc/hosts #2184

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42 changes: 29 additions & 13 deletions docs/containers.conf.5.md
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Original file line number Diff line number Diff line change
Expand Up @@ -96,10 +96,12 @@ The default profile name is "container-default".

**base_hosts_file**=""

The hosts entries from the base hosts file are added to the containers hosts
file. This must be either an absolute path or as special values "image" which
uses the hosts file from the container image or "none" which means
no base hosts file is used. The default is "" which will use /etc/hosts.
Base file to create the `/etc/hosts` file inside the container. This must either
be an absolute path to a file on the host system, or one of the following
special flags:
"" Use the host's `/etc/hosts` file (the default)
`none` Do not use a base file (i.e. start with an empty file)
`image` Use the container image's `/etc/hosts` file as base file

**cgroup_conf**=[]

Expand Down Expand Up @@ -195,13 +197,25 @@ Pass all host environment variables into the container.

**host_containers_internal_ip**=""

Set the ip for the host.containers.internal entry in the containers /etc/hosts
file. This can be set to "none" to disable adding this entry. By default it
will automatically choose the host ip.

NOTE: When using podman machine this entry will never be added to the containers
hosts file instead the gvproxy dns resolver will resolve this hostname. Therefore
it is not possible to disable the entry in this case.
Set the IP address the container should expect to connect to the host. The IP
address is used by Podman to automatically add the `host.containers.internal`
and `host.docker.internal` hostnames to the container's `/etc/hosts` file. It
is also used for the *host-gateway* flag of Podman's `--add-host` CLI option.
If no IP address is configured (the default), Podman will try to determine it
automatically, but might fail to do so depending on the container's network
setup. Adding these internal hostnames to `/etc/hosts` is silently skipped then.
Set this config to `none` to never add the internal hostnames to `/etc/hosts`.

Note: If Podman is running in a virtual machine using `podman machine` (this
includes Mac and Windows hosts), Podman will silently skip adding the internal
hostnames to `/etc/hosts`, unless an IP address was configured manually. The
internal hostnames are resolved by the gvproxy DNS resolver instead. This config
has no effect on gvproxy. However, since `/etc/hosts` bypasses the DNS resolver,
a manually configured IP address still takes precedence.

Note: This config doesn't affect the actual network setup, it just tells Podman
the IP address it should expect. Configuring an IP address here doesn't ensure
that the container can actually reach the host using this IP address.

**http_proxy**=true

Expand Down Expand Up @@ -290,8 +304,10 @@ Options are:

**no_hosts**=false

Create /etc/hosts for the container. By default, container engines manage
/etc/hosts, automatically adding the container's own IP address.
Do not modify the `/etc/hosts` file in the container. Podman assumes control
over the container's `/etc/hosts` file by default; refer to the `--add-host`
CLI option for details. To disable this, either set this config to `true`, or
use the functionally identical `--no-hosts` CLI option.

**oom_score_adj**=0

Expand Down
43 changes: 30 additions & 13 deletions pkg/config/containers.conf
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Expand Up @@ -27,16 +27,19 @@
#
#apparmor_profile = "container-default"

# The hosts entries from the base hosts file are added to the containers hosts
# file. This must be either an absolute path or as special values "image" which
# uses the hosts file from the container image or "none" which means
# no base hosts file is used. The default is "" which will use /etc/hosts.
# Base file to create the `/etc/hosts` file inside the container. This must either
# be an absolute path to a file on the host system, or one of the following
# special flags:
# "" Use the host's `/etc/hosts` file (the default)
# `none` Do not use a base file (i.e. start with an empty file)
# `image` Use the container image's `/etc/hosts` file as base file
#
#base_hosts_file = ""

# List of cgroup_conf entries specifying a list of cgroup files to write to and
# their values. For example `memory.high=1073741824` sets the
# memory.high limit to 1GB.
#
# cgroup_conf = []

# Default way to to create a cgroup namespace for the container
Expand Down Expand Up @@ -126,13 +129,25 @@ default_sysctls = [
#
#env_host = false

# Set the ip for the host.containers.internal entry in the containers /etc/hosts
# file. This can be set to "none" to disable adding this entry. By default it
# will automatically choose the host ip.
#
# NOTE: When using podman machine this entry will never be added to the containers
# hosts file instead the gvproxy dns resolver will resolve this hostname. Therefore
# it is not possible to disable the entry in this case.
# Set the IP address the container should expect to connect to the host. The IP
# address is used by Podman to automatically add the `host.containers.internal`
# and `host.docker.internal` hostnames to the container's `/etc/hosts` file. It
# is also used for the *host-gateway* flag of Podman's `--add-host` CLI option.
# If no IP address is configured (the default), Podman will try to determine it
# automatically, but might fail to do so depending on the container's network
# setup. Adding these internal hostnames to `/etc/hosts` is silently skipped then.
# Set this config to `none` to never add the internal hostnames to `/etc/hosts`.
#
# Note: If Podman is running in a virtual machine using `podman machine` (this
# includes Mac and Windows hosts), Podman will silently skip adding the internal
# hostnames to `/etc/hosts`, unless an IP address was configured manually. The
# internal hostnames are resolved by the gvproxy DNS resolver instead. This config
# has no effect on gvproxy. However, since `/etc/hosts` bypasses the DNS resolver,
# a manually configured IP address still takes precedence.
#
# Note: This config doesn't affect the actual network setup, it just tells Podman
# the IP address it should expect. Configuring an IP address here doesn't ensure
# that the container can actually reach the host using this IP address.
#
#host_containers_internal_ip = ""

Expand Down Expand Up @@ -221,8 +236,10 @@ default_sysctls = [
#
#netns = "private"

# Create /etc/hosts for the container. By default, container engine manage
# /etc/hosts, automatically adding the container's own IP address.
# Do not modify the `/etc/hosts` file in the container. Podman assumes control
# over the container's `/etc/hosts` file by default; refer to the `--add-host`
# CLI option for details. To disable this, either set this config to `true`, or
# use the functionally identical `--no-hosts` CLI option.
#
#no_hosts = false

Expand Down