Consider the exact sequence of finite flat group schemes over the $2$-adic integers ring $\mathbb{Z}_2$: $$0\longrightarrow\mathbb{Z}/2\mathbb{Z}\longrightarrow A\longrightarrow\mathbb{Z}/2\mathbb{Z}\longrightarrow0.$$
$\textbf{Question}$: Why is $A$ étale?
The motivation is that if I know $A$ is étale, but we also know $\mathbb{Z}_2$ is a complete DVR, and any finite étale group scheme over such a ring is constant, so I can derive $A$ is a constant group scheme.
Thanks!