94 lines
2.4 KiB
ReStructuredText
94 lines
2.4 KiB
ReStructuredText
Messaging
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=========
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Description
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-----------
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cdist has a simple but powerful way of allowing communication between
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the initial manifest and types as well as types and types.
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Whenever execution is passed from cdist to one of the
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scripts described below, cdist generate 2 new temporary files
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and exports the environment variables **__messages_in** and
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**__messages_out** to point to them.
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Before handing over the control, the content of the global message
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file is copied into the file referenced by **$__messages_in**.
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After cdist gained control back, the content of the file referenced
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by **$__messages_out** is appended to the global message file.
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This way overwriting any of the two files by accident does not
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interfere with other types.
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The order of execution is not defined unless you create dependencies
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between the different objects (see `cdist manifest <cdist-manifest.html>`_) and thus you
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can only react reliably on messages by objects that you depend on.
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Availability
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------------
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Messaging is possible between all **local** scripts:
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- initial manifest
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- type/manifest
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- type/gencode-local
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- type/gencode-remote
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Examples
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--------
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When you want to emit a message use:
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.. code-block:: sh
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echo "something" >> "$__messages_out"
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When you want to react on a message use:
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.. code-block:: sh
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if grep -q "^__your_type/object/id:something" "$__messages_in"; then
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echo "I do something else"
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fi
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Some real life examples:
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.. code-block:: sh
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# Reacting on changes from block for keepalive
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if grep -q "^__block/keepalive-vrrp" "$__messages_in"; then
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echo /etc/init.d/keepalived restart
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fi
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# Reacting on changes of configuration files
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if grep -q "^__file/etc/one" $__messages_in; then
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echo 'for init in /etc/init.d/opennebula*; do $init restart; done'
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fi
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Restart sshd on changes
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.. code-block:: sh
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os="$(cat "$__global/explorer/os")"
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case "$os" in
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centos|redhat|suse)
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restart="/etc/init.d/sshd restart"
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;;
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debian|ubuntu)
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restart="/etc/init.d/ssh restart"
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;;
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*)
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cat << eof >&2
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Unsupported os $os.
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If you would like to have this type running on $os,
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you can either develop the changes and send a pull
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request or ask for a quote at www.ungleich.ch
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eof
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exit 1
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;;
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esac
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if grep -q "^__key_value/PermitRootLogin" "$__messages_in"; then
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echo $restart
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fi
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