terraform libvirt: document usage

Signed-off-by: Malte Poll <mp@edgeless.systems>

terraform/libvirt/README.md

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+# Local image testing with QEMU / libvirt / terraform
+
+## Usage
+
+Prerequisite:
+
+- [qcow2 constellation image](/image/)
+- [setup](#setup-libvirt--terraform)
+
+Optional: Write a `terraform.tfvars` file in the terraform workspace (`terraform/libvirt`), defining required variables and overriding optional variables.
+See [variables.tf](./variables.tf) for a description of all available variables.
+```tfvars
+constellation_coreos_image_qcow2="/path/to/image.qcow2"
+# optional other vars, uncomment and change as needed
+# control_plane_count=3
+# worker_count=2
+# vcpus=2
+# memory=2048
+# state_disk_size=10
+# ip_range_start=100
+```
+
+Create terraform resources from within terraform workspace (`terraform/libvirt`):
+```shell-session
+cd terraform/libvirt
+terraform init
+terraform plan
+terraform apply
+
+# set CONST_DIR to your constellation workspace
+export TF_DIR=$(pwd)
+export CONST_DIR=$(pwd)
+go run ../../hack/terraform-to-state/create-state.go  "${TF_DIR}" "${CONST_DIR}"
+
+# use constellation (everything after constellation create)
+constellation config generate qemu
+# run cdbg if using a debug image
+cdbg deploy
+constellation init
+
+# cleanup
+rm constellation-state.json constellation-mastersecret.base64 constellation-admin.conf wg0.conf
+terraform destroy
+```
+
+## Setup libvirt & Terraform
+
+<details>
+<summary>Ubuntu</summary>
+
+[General reference](https://ubuntu.com/server/docs/virtualization-libvirt)
+```shell-session
+# Install Terraform
+curl -fsSL https://apt.releases.hashicorp.com/gpg | sudo apt-key add -
+sudo apt-add-repository "deb [arch=amd64] https://apt.releases.hashicorp.com $(lsb_release -cs) main"
+sudo apt-get update && sudo apt-get install terraform
+# install libvirt, KVM and tools
+sudo apt install qemu-kvm libvirt-daemon-system xsltproc
+sudo systemctl enable libvirtd
+sudo usermod -a -G libvirt $USER
+# reboot
+```
+</details>
+
+<details>
+<summary>Fedora</summary>
+
+```shell-session
+sudo dnf install -y dnf-plugins-core
+sudo dnf config-manager --add-repo https://rpm.releases.hashicorp.com/fedora/hashicorp.repo
+sudo dnf -y install terraform qemu-kvm libvirt-daemon-config-network libvirt-daemon-kvm xsltproc
+sudo usermod -a -G libvirt $USER
+# reboot
+```
+</details>
+
+## Change libvirt settings (on Ubuntu)
+Open `/etc/libvirt/qemu.conf` and change the following settings:
+
+```
+security_driver = "none"
+```
+Then restart libvirt
+
+```shell-session
+sudo systemctl restart libvirtd
+```
+
+## Setup emulated TPM (on Ubuntu)
+Only works if swtpm is version 0.7 or newer!
+Ubuntu currently ships swtpm 0.6.3 so you need to install swtpm [from launchpad](https://launchpad.net/~stefanberger/+archive/ubuntu/swtpm-jammy/).
+
+1. Uninstall current version of swtpm (if installed)
+	```
+	sudo apt remove swtpm swtpm-tools
+	```
+2. Add ppa (this command shows the ppa for Ubuntu 22.04 jammy but others are available)
+	```
+	sudo add-apt-repository ppa:stefanberger/swtpm-jammy
+	sudo apt update
+	```
+3. Install swtpm
+	```
+	sudo apt install swtpm swtpm-tools
+	```
+4. Patch configuration under `/etc/swtpm_setup.conf`
+	```
+	# Program invoked for creating certificates
+	create_certs_tool = /usr/bin/swtpm_localca
+	```
+5. Patch ownership of `/var/lib/swtpm-localca`
+   ```shell-session
+   sudo chown -R swtpm:root /var/lib/swtpm-localca
+   ```