6df7921cb7
When using simple-init, we are making an explicit choice along the lines of "I want the simple tool to do the simple needful" which works well, except when cloud-init tries to run because it is already baked into the source image diskimage-builder started with. So what would happen is Glean would execute from simple-init, and then cloud-init would get launched by default, and cloud-init in some cases everything is DHCP, so suddenly any static configuration, such as what might be in an attached configuration drive, is stomped upon resulting in an unreachable instance if DHCP is just not available. If DHCP is available, generally this is not an issue and goes un-noticed, yet can add a substantial amount of time to the boot sequence "waiting" for meta-data endpoints which may not exist. Change-Id: I380b9638cd28f5771530089c558ef5ab638c0173
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3.1 KiB
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85 lines
3.1 KiB
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===========
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simple-init
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===========
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Basic network and system configuration that can't be done until boot
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Unfortunately, as much as we'd like to bake it in to an image, we can't
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know in advance how many network devices will be present, nor if DHCP is
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present in the host cloud. Additionally, in environments where cloud-init
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is not used, there are a couple of small things, like mounting config-drive
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and pulling ssh keys from it, that need to be done at boot time.
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.. note::
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This element removes cloud-init as it can stomp on the configuration
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applied by glean, resulting in additional problems for operators,
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and a more difficult path troubleshooting.
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Autodetect network interfaces during boot and configure them
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------------------------------------------------------------
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The rationale for this is that we are likely to require multiple
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network interfaces for use cases such as baremetal and there is no way
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to know ahead of time which one is which, so we will simply run a
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DHCP client on all interfaces with real MAC addresses (except lo) that
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are visible on the first boot.
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The script `/usr/local/sbin/simple-init.sh` will be called
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early in each boot and will scan available network interfaces and
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ensure they are configured properly before networking services are started.
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Processing startup information from config-drive
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------------------------------------------------
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On most systems, the DHCP approach desribed above is fine. But in some clouds,
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such as Rackspace Public cloud, there is no DHCP. Instead, there is static
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network config via `config-drive`. `simple-init` will happily call
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`glean` which will do nothing if static network information is
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not there.
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Finally, glean will handle ssh-keypair-injection from config
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drive if cloud-init is not installed.
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Chosing glean installation source
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---------------------------------
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By default glean is installed using pip using the latest release on pypi.
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It is also possible to install glean from a specified git repository
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location. This is useful for debugging and testing new glean changes
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for example. To do this you need to set these variables::
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DIB_INSTALLTYPE_simple_init=repo
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DIB_REPOLOCATION_glean=/path/to/glean/repo
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DIB_REPOREF_glean=name_of_git_ref
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For example to test glean change 364516 do::
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git clone https://opendev.org/opendev/glean /tmp/glean
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cd /tmp/glean
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git review -d 364516
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git checkout -b my-test-ref
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Then set your DIB env vars like this before running DIB::
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DIB_INSTALLTYPE_simple_init=repo
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DIB_REPOLOCATION_glean=/tmp/glean
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DIB_REPOREF_glean=my-test-ref
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NetworkManager
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--------------
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By default, this uses the "legacy" scripts on each platform. To use
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NetworkManager instead, set ``DIB_SIMPLE_INIT_NETWORKMANAGER`` to
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non-zero. See the glean documentation for what the implications for
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this are on each platform.
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This is currently only implemented for CentOS and Fedora platforms.
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Fallback
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--------
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Glean falls back to DHCPv4 for all interfaces that do not have an explicit
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configuration. If this is not desired, set the following variable to disable
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the fallback and leave such interfaces unconfigured::
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export DIB_SIMPLE_INIT_NO_DHCP_FALLBACK=1
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