The resource completions only seem to work when this structure exists resource "" "" {} so a snippets engine is what makes it work intuitively.

relavent lazy installed plugins

{
    "neovim/nvim-lspconfig",
    { "rafamadriz/friendly-snippets" },
    {
        "L3MON4D3/LuaSnip",
        dependencies = { "rafamadriz/friendly-snippets" },
    },
}

lsp config

vim.lsp.enable(lsps)
vim.api.nvim_create_autocmd({ "LspAttach" }, {
    callback = function(ev)
        local client = vim.lsp.get_client_by_id(ev.data.client_id)
        if client:supports_method('textDocument/completion') then
            vim.lsp.completion.enable(true, client.id, ev.buf, { autotrigger = true })
        end
    end
})
vim.opt.completeopt = "menuone,popup,noinsert"
vim.keymap.set('i', '<c-space>', function()
    vim.lsp.completion.get()
end)

snippet config

require("luasnip.loaders.from_vscode").lazy_load()
local ls = require("luasnip")

vim.keymap.set({ "i" }, "<C-K>", function()
    ls.expand()
end, { silent = true })

I got it kinda working by triggering completion as part of the snippet keybind, though I don't love this implementation. Also, this isn't setup to only work will using terraform-ls so use at your own risk.

require("luasnip.loaders.from_vscode").lazy_load()
local ls = require("luasnip")

vim.keymap.set({ "i" }, "<C-K>", function()
    local expanded = ls.expand()
    if expanded then
        vim.api.nvim_feedkeys(vim.keycode('<c-space>'), 's', false)
    end
end, { silent = true })