I think also a very good way to earn a nice passive income is investing in Cryptocurrency, especially in Masternode Cryptocurrencies, which provide a passive income in coins, also those carefully picked coins grow in value, so it’s a double gain! And a great coin to invest in at the moment is GINCOIN, which is the fuel for a really succesful project. Find more at GINCOIN Website: https://gincoin.io/ 😉
To your point about Municipal Bonds, my concern is tax reform. While everything is mostly being worked behind closed doors (and likely wont ever see the light of day). There is still the chance they propose to limit the amount of the tax free nature of these bonds. While I dont sen panic in the streets, I do see a scenario where bond prices get additional pressure because municipalities have to increase rates due to people putting their money to work elsewhere.

Indoor air pollution resulting from the use of solid fuels [by poorer segments of society] is a major killer. It claims the lives of 1.5 million people each year, more than half of them below the age of five: that is 4000 deaths a day. To put this number in context, it exceeds total deaths from malaria and rivals the number of deaths from tuberculosis.Source 15

At age 55, I own high-end rental properties (near the beach) and commercial buildings servicing the medical industry. I was widely criticized during my career for not living up to my income; that is, buying big homes with many fancy cars. I married a great woman who understood that saving and investing today meant a better lifestyle and more freedom tomorrow. Our passive income is half of my active income from sales, but my net worth has increased substantially. We are both happier and healthier than we were in the high-stress pressure cooker of franchise sales. The naysayers have become converts to the concept of passive income, but they have locked themselves into a “big hat, no cattle” lifestyle. It has been a great ride!
India is one of the largest centres for polishing diamonds and gems and manufacturing jewellery; it is also one of the two largest consumers of gold.[183][184] After crude oil and petroleum products, the export and import of gold, precious metals, precious stones, gems and jewellery accounts for the largest portion of India's global trade. The industry contributes about 7% of India's GDP, employs millions, and is a major source of its foreign-exchange earnings.[185] The gems and jewellery industry, in 2013, created ₹251,000 crore (US$35 billion) in economic output on value-added basis. It is growing sector of Indian economy, and A.T. Kearney projects it to grow to ₹500,000 crore (US$70 billion) by 2018.[186]
The term Multiple Streams of Income in a way voices and explains itself. It’s the theory of earning more than one type of income from more than one source. Generating multiple sources of income is a key to wealth creation, it becomes even more special when you’re doing it with a passive income which does not really require a lot of time and efforts from you (We’ll talk more about that later).
Portfolio income can come from multiple sources – interest/bond coupons, stock dividends, financial strategies including derivatives and capital growth.  Each offers some cash flow and some also offer potential capital gain with some risk from liquidity and volatile prices.  In this low-yield environment, many investors rely too heavily on cash flows and to pursue this are venturing further into riskier areas than they’d normally consider.